To allow the userspace to test many hardware configuration, introduce a
new interface to configure the available formats per planes. VKMS supports
multiple formats, so the userspace can choose any combination.

The supported formats are configured by writing the fourcc code in
supported_formats:
 # enable AR24 format
  echo '+AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
 # disable AR24 format
  echo '-AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
 # enable all format supported by VKMS
  echo '+*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
 # disable all formats
  echo '-*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats

Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
---
 Documentation/ABI/testing/configfs-vkms         |   9 ++
 Documentation/gpu/vkms.rst                      |   7 +-
 drivers/gpu/drm/vkms/tests/Makefile             |   3 +-
 drivers/gpu/drm/vkms/tests/vkms_configfs_test.c | 102 ++++++++++++++++++++
 drivers/gpu/drm/vkms/vkms_configfs.c            | 118 ++++++++++++++++++++++++
 drivers/gpu/drm/vkms/vkms_configfs.h            |   6 ++
 6 files changed, 243 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
index 2ace79ce848a..48f92538c602 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -153,6 +153,15 @@ Description:
         Default color range presented to userspace, same
         values as supported_color_ranges.
 
+What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
+Date:		Nov 2025
+Contact:	dri-devel@lists.freedesktop.org
+Description:
+        List of supported formats for this plane. To add a new
+        item, write its fourcc code prefixed with '+'. To remove,
+        use '-' prefix. Use '+*' to add all formats, '-*' to
+        remove all.
+
 What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
 Date:		Nov 2025
 Contact:	dri-devel@lists.freedesktop.org
diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index ab0eb2f97fc2..15d62ad963c9 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -87,7 +87,7 @@ Start by creating one or more planes::
 
   sudo mkdir /config/vkms/my-vkms/planes/plane0
 
-Planes have 8 configurable attributes:
+Planes have 9 configurable attributes:
 
 - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
   exposed by the "type" property of a plane)
@@ -109,6 +109,11 @@ Planes have 8 configurable attributes:
   must be set too.
 - default_color_range: Default color range presented to the userspace, same
   values as supported_color_ranges
+- supported_formats: List of supported formats for this plane. To add a new item in the
+  list, write it using a plus and fourcc code: +XR24
+  To remove a format, use a minus and its fourcc: -XR24
+  To add all formats use +*
+  To remove all formats, use -*
 
 Continue by creating one or more CRTCs::
 
diff --git a/drivers/gpu/drm/vkms/tests/Makefile b/drivers/gpu/drm/vkms/tests/Makefile
index d4d9ba8d4c54..92cfa7262ba4 100644
--- a/drivers/gpu/drm/vkms/tests/Makefile
+++ b/drivers/gpu/drm/vkms/tests/Makefile
@@ -3,6 +3,7 @@
 vkms-kunit-tests-y := \
 	vkms_config_test.o \
 	vkms_format_test.o \
-	vkms_color_test.o
+	vkms_color_test.o \
+	vkms_configfs_test.o \
 
 obj-$(CONFIG_DRM_VKMS_KUNIT_TEST) += vkms-kunit-tests.o
diff --git a/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
new file mode 100644
index 000000000000..8d02c2c459d9
--- /dev/null
+++ b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include "linux/printk.h"
+#include <kunit/test.h>
+
+#include "../vkms_configfs.h"
+
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
+
+/**
+ * struct vkms_configfs_parse_format_case - Store test case for format parsing
+ * @str: Contains the string to parse
+ * @str_len: str len
+ * @expected_len: expected len of the matched format
+ * @expected_offset: expected offset in the string for the parsed format
+ */
+struct vkms_configfs_parse_format_case {
+	const char *str;
+	int str_len;
+	int expected_len;
+	int expected_offset;
+};
+
+struct vkms_configfs_parse_format_case vkms_configfs_parse_format_test_cases[] = {
+	{
+		.str = "+RG24",
+		.str_len = 6,
+		.expected_len = 5,
+		.expected_offset = 0,
+	}, {
+		.str = "-RG24",
+		.str_len = 6,
+		.expected_len = 5,
+		.expected_offset = 0
+	}, {
+		.str = "  -RG24",
+		.str_len = 8,
+		.expected_len = 5,
+		.expected_offset = 2
+	}, {
+		.str = "+*",
+		.str_len = 3,
+		.expected_len = 2,
+		.expected_offset = 0
+	}, {
+		.str = "-RG24+RG24",
+		.str_len = 11,
+		.expected_len = 5,
+		.expected_offset = 0
+	}, {
+		.str = "-R1+RG24",
+		.str_len = 9,
+		.expected_len = 3,
+		.expected_offset = 0
+	}, {
+		.str = "\n-R1",
+		.str_len = 5,
+		.expected_len = 3,
+		.expected_offset = 1
+	}, {
+		.str = "-R1111",
+		.str_len = 3,
+		.expected_len = 3,
+		.expected_offset = 0
+	}
+};
+
+static void vkms_configfs_test_parse_format(struct kunit *test)
+{
+	const struct vkms_configfs_parse_format_case *param = test->param_value;
+	char *out;
+	int len = vkms_configfs_parse_next_format(param->str, param->str + param->str_len, &out);
+
+	KUNIT_EXPECT_EQ(test, len, param->expected_len);
+	KUNIT_EXPECT_PTR_EQ(test, out, param->str + param->expected_offset);
+}
+
+static void vkms_configfs_test_parse_format_get_desc(struct vkms_configfs_parse_format_case *t,
+						     char *desc)
+{
+	snprintf(desc, KUNIT_PARAM_DESC_SIZE, "%s", t->str);
+}
+
+KUNIT_ARRAY_PARAM(vkms_configfs_test_parse_format, vkms_configfs_parse_format_test_cases,
+		  vkms_configfs_test_parse_format_get_desc
+);
+
+static struct kunit_case vkms_configfs_test_cases[] = {
+	KUNIT_CASE_PARAM(vkms_configfs_test_parse_format,
+			 vkms_configfs_test_parse_format_gen_params),
+	{}
+};
+
+static struct kunit_suite vkms_configfs_test_suite = {
+	.name = "vkms-configfs",
+	.test_cases = vkms_configfs_test_cases,
+};
+
+kunit_test_suite(vkms_configfs_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Kunit test for vkms configfs utility");
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 7be6d10b2b68..a451d1122acf 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -3,6 +3,8 @@
 #include <linux/configfs.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/string.h>
+#include <kunit/visibility.h>
 
 #include "vkms_drv.h"
 #include "vkms_config.h"
@@ -628,6 +630,120 @@ static ssize_t plane_default_color_encoding_store(struct config_item *item,
 	return count;
 }
 
+static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	page[0] = '\0';
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		u32 *formats = vkms_config_plane_get_supported_formats(plane->config);
+
+		for (int i = 0;
+		     i < vkms_config_plane_get_supported_formats_count(plane->config);
+		     i++) {
+			char tmp[6] = { 0 };
+			const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
+					       (int)sizeof(*formats),
+					       (char *)&formats[i]);
+			if (ret < 0)
+				return ret;
+			/*
+			 * Limitation of ConfigFS attributes, an attribute can't be bigger
+			 * than PAGE_SIZE. This will crop the result if this plane support
+			 * more than ≈1000 formats.
+			 */
+			if (ret + strlen(page) > PAGE_SIZE - 1)
+				return -ENOMEM;
+			strncat(page, tmp, ARRAY_SIZE(tmp));
+		}
+	}
+
+	return strlen(page);
+}
+
+/**
+ * parse_next_format() - Parse the next format in page, skipping all non fourcc-related characters
+ * @page: page to search into
+ * @page_end: last character of the page
+ * @out: Output pointer, will point inside page
+ *
+ * Returns: size of the matched format, @out will point to the + or -
+ */
+VISIBLE_IF_KUNIT
+int vkms_configfs_parse_next_format(const char *page, const char *page_end, char **out)
+{
+	int count = page - page_end;
+	char *tmp_plus = strnchr(page, count, '+');
+	char *tmp_minus = strnchr(page, count, '-');
+
+	if (!tmp_plus && !tmp_minus)
+		return 0;
+	if (!tmp_plus)
+		*out = tmp_minus;
+	else if (!tmp_minus)
+		*out = tmp_plus;
+	else
+		*out = min(tmp_plus, tmp_minus);
+
+	char *end = *out + 1;
+
+	while (end < page_end) {
+		if (!isalnum(*end) && *end != '*')
+			break;
+		end++;
+	}
+
+	return end - *out;
+}
+EXPORT_SYMBOL_IF_KUNIT(vkms_configfs_parse_next_format);
+
+static ssize_t plane_supported_formats_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct vkms_configfs_plane *plane;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+	int ret = 0;
+	const char *end_page = page + count;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		while (1) {
+			char *tmp;
+			char fmt[4] = {' ', ' ', ' ', ' '};
+			int len = vkms_configfs_parse_next_format(page, end_page, &tmp);
+
+			// No fourcc code found
+			if (len <= 1 || len > 5)
+				break;
+
+			page = tmp + len;
+			memcpy(fmt, &tmp[1], min(len - 1, 4));
+			if (tmp[0] == '+') {
+				if (fmt[0] == '*') {
+					ret = vkms_config_plane_add_all_formats(plane->config);
+					if (ret)
+						return ret;
+				} else {
+					ret = vkms_config_plane_add_format(plane->config,
+									   *(int *)fmt);
+					if (ret)
+						return ret;
+				}
+			} else if (tmp[0] == '-') {
+				if (fmt[0] == '*')
+					vkms_config_plane_remove_all_formats(plane->config);
+				else
+					vkms_config_plane_remove_format(plane->config, *(int *)fmt);
+			}
+		}
+	}
+
+	return count;
+}
+
 CONFIGFS_ATTR(plane_, type);
 CONFIGFS_ATTR(plane_, name);
 CONFIGFS_ATTR(plane_, supported_rotations);
@@ -636,6 +752,7 @@ CONFIGFS_ATTR(plane_, supported_color_ranges);
 CONFIGFS_ATTR(plane_, default_color_range);
 CONFIGFS_ATTR(plane_, supported_color_encodings);
 CONFIGFS_ATTR(plane_, default_color_encoding);
+CONFIGFS_ATTR(plane_, supported_formats);
 
 static struct configfs_attribute *plane_item_attrs[] = {
 	&plane_attr_type,
@@ -646,6 +763,7 @@ static struct configfs_attribute *plane_item_attrs[] = {
 	&plane_attr_default_color_range,
 	&plane_attr_supported_color_encodings,
 	&plane_attr_default_color_encoding,
+	&plane_attr_supported_formats,
 	NULL,
 };
 
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.h b/drivers/gpu/drm/vkms/vkms_configfs.h
index e9020b0043db..2774655bfcc5 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.h
+++ b/drivers/gpu/drm/vkms/vkms_configfs.h
@@ -2,7 +2,13 @@
 #ifndef _VKMS_CONFIGFS_H_
 #define _VKMS_CONFIGFS_H_
 
+#include <linux/types.h>
+
 int vkms_configfs_register(void);
 void vkms_configfs_unregister(void);
 
+#if IS_ENABLED(CONFIG_KUNIT)
+int vkms_configfs_parse_next_format(const char *page, const char *end_page, char **out);
+#endif
+
 #endif /* _VKMS_CONFIGFS_H_ */

-- 
2.51.2

On Mon, Dec 22, 2025 at 11:11:20AM +0100, Louis Chauvet wrote:
> To allow the userspace to test many hardware configuration, introduce a
> new interface to configure the available formats per planes. VKMS supports
> multiple formats, so the userspace can choose any combination.
> 
> The supported formats are configured by writing the fourcc code in
> supported_formats:
>  # enable AR24 format
>   echo '+AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable AR24 format
>   echo '-AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # enable all format supported by VKMS
>   echo '+*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable all formats
>   echo '-*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  Documentation/ABI/testing/configfs-vkms         |   9 ++
>  Documentation/gpu/vkms.rst                      |   7 +-
>  drivers/gpu/drm/vkms/tests/Makefile             |   3 +-
>  drivers/gpu/drm/vkms/tests/vkms_configfs_test.c | 102 ++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_configfs.c            | 118 ++++++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_configfs.h            |   6 ++
>  6 files changed, 243 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
> index 2ace79ce848a..48f92538c602 100644
> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -153,6 +153,15 @@ Description:
>          Default color range presented to userspace, same
>          values as supported_color_ranges.
>  
> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
> +Date:		Nov 2025
> +Contact:	dri-devel@lists.freedesktop.org
> +Description:
> +        List of supported formats for this plane. To add a new
> +        item, write its fourcc code prefixed with '+'. To remove,
> +        use '-' prefix. Use '+*' to add all formats, '-*' to
> +        remove all.
> +
>  What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>  Date:		Nov 2025
>  Contact:	dri-devel@lists.freedesktop.org
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index ab0eb2f97fc2..15d62ad963c9 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,7 +87,7 @@ Start by creating one or more planes::
>  
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>  
> -Planes have 8 configurable attributes:
> +Planes have 9 configurable attributes:
>  
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> @@ -109,6 +109,11 @@ Planes have 8 configurable attributes:
>    must be set too.
>  - default_color_range: Default color range presented to the userspace, same
>    values as supported_color_ranges
> +- supported_formats: List of supported formats for this plane. To add a new item in the
> +  list, write it using a plus and fourcc code: +XR24
> +  To remove a format, use a minus and its fourcc: -XR24
> +  To add all formats use +*
> +  To remove all formats, use -*
>  
>  Continue by creating one or more CRTCs::
>  
> diff --git a/drivers/gpu/drm/vkms/tests/Makefile b/drivers/gpu/drm/vkms/tests/Makefile
> index d4d9ba8d4c54..92cfa7262ba4 100644
> --- a/drivers/gpu/drm/vkms/tests/Makefile
> +++ b/drivers/gpu/drm/vkms/tests/Makefile
> @@ -3,6 +3,7 @@
>  vkms-kunit-tests-y := \
>  	vkms_config_test.o \
>  	vkms_format_test.o \
> -	vkms_color_test.o
> +	vkms_color_test.o \
> +	vkms_configfs_test.o \
>  
>  obj-$(CONFIG_DRM_VKMS_KUNIT_TEST) += vkms-kunit-tests.o
> diff --git a/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
> new file mode 100644
> index 000000000000..8d02c2c459d9
> --- /dev/null
> +++ b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include "linux/printk.h"
> +#include <kunit/test.h>
> +
> +#include "../vkms_configfs.h"
> +
> +MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
> +
> +/**
> + * struct vkms_configfs_parse_format_case - Store test case for format parsing
> + * @str: Contains the string to parse
> + * @str_len: str len
> + * @expected_len: expected len of the matched format
> + * @expected_offset: expected offset in the string for the parsed format
> + */
> +struct vkms_configfs_parse_format_case {
> +	const char *str;
> +	int str_len;
> +	int expected_len;
> +	int expected_offset;
> +};
> +
> +struct vkms_configfs_parse_format_case vkms_configfs_parse_format_test_cases[] = {
> +	{
> +		.str = "+RG24",
> +		.str_len = 6,
> +		.expected_len = 5,
> +		.expected_offset = 0,
> +	}, {
> +		.str = "-RG24",
> +		.str_len = 6,
> +		.expected_len = 5,
> +		.expected_offset = 0
> +	}, {
> +		.str = "  -RG24",
> +		.str_len = 8,
> +		.expected_len = 5,
> +		.expected_offset = 2
> +	}, {
> +		.str = "+*",
> +		.str_len = 3,
> +		.expected_len = 2,
> +		.expected_offset = 0
> +	}, {
> +		.str = "-RG24+RG24",
> +		.str_len = 11,
> +		.expected_len = 5,
> +		.expected_offset = 0
> +	}, {
> +		.str = "-R1+RG24",
> +		.str_len = 9,
> +		.expected_len = 3,
> +		.expected_offset = 0
> +	}, {
> +		.str = "\n-R1",
> +		.str_len = 5,
> +		.expected_len = 3,
> +		.expected_offset = 1
> +	}, {
> +		.str = "-R1111",
> +		.str_len = 3,
> +		.expected_len = 3,
> +		.expected_offset = 0
> +	}
> +};
> +
> +static void vkms_configfs_test_parse_format(struct kunit *test)
> +{
> +	const struct vkms_configfs_parse_format_case *param = test->param_value;
> +	char *out;
> +	int len = vkms_configfs_parse_next_format(param->str, param->str + param->str_len, &out);
> +
> +	KUNIT_EXPECT_EQ(test, len, param->expected_len);
> +	KUNIT_EXPECT_PTR_EQ(test, out, param->str + param->expected_offset);
> +}
> +
> +static void vkms_configfs_test_parse_format_get_desc(struct vkms_configfs_parse_format_case *t,
> +						     char *desc)
> +{
> +	snprintf(desc, KUNIT_PARAM_DESC_SIZE, "%s", t->str);
> +}
> +
> +KUNIT_ARRAY_PARAM(vkms_configfs_test_parse_format, vkms_configfs_parse_format_test_cases,
> +		  vkms_configfs_test_parse_format_get_desc
> +);
> +
> +static struct kunit_case vkms_configfs_test_cases[] = {
> +	KUNIT_CASE_PARAM(vkms_configfs_test_parse_format,
> +			 vkms_configfs_test_parse_format_gen_params),
> +	{}
> +};
> +
> +static struct kunit_suite vkms_configfs_test_suite = {
> +	.name = "vkms-configfs",
> +	.test_cases = vkms_configfs_test_cases,
> +};
> +
> +kunit_test_suite(vkms_configfs_test_suite);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Kunit test for vkms configfs utility");
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 7be6d10b2b68..a451d1122acf 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -3,6 +3,8 @@
>  #include <linux/configfs.h>
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
> +#include <linux/string.h>
> +#include <kunit/visibility.h>
>  
>  #include "vkms_drv.h"
>  #include "vkms_config.h"
> @@ -628,6 +630,120 @@ static ssize_t plane_default_color_encoding_store(struct config_item *item,
>  	return count;
>  }
>  
> +static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	page[0] = '\0';
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		u32 *formats = vkms_config_plane_get_supported_formats(plane->config);
> +
> +		for (int i = 0;
> +		     i < vkms_config_plane_get_supported_formats_count(plane->config);
> +		     i++) {
> +			char tmp[6] = { 0 };
> +			const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
> +					       (int)sizeof(*formats),
> +					       (char *)&formats[i]);
> +			if (ret < 0)
> +				return ret;
> +			/*
> +			 * Limitation of ConfigFS attributes, an attribute can't be bigger
> +			 * than PAGE_SIZE. This will crop the result if this plane support
> +			 * more than ≈1000 formats.
> +			 */
> +			if (ret + strlen(page) > PAGE_SIZE - 1)
> +				return -ENOMEM;
> +			strncat(page, tmp, ARRAY_SIZE(tmp));
> +		}
> +	}
> +
> +	return strlen(page);
> +}
> +
> +/**
> + * parse_next_format() - Parse the next format in page, skipping all non fourcc-related characters
> + * @page: page to search into
> + * @page_end: last character of the page
> + * @out: Output pointer, will point inside page
> + *
> + * Returns: size of the matched format, @out will point to the + or -
> + */
> +VISIBLE_IF_KUNIT
> +int vkms_configfs_parse_next_format(const char *page, const char *page_end, char **out)
> +{
> +	int count = page - page_end;
> +	char *tmp_plus = strnchr(page, count, '+');
> +	char *tmp_minus = strnchr(page, count, '-');
> +
> +	if (!tmp_plus && !tmp_minus)
> +		return 0;
> +	if (!tmp_plus)
> +		*out = tmp_minus;
> +	else if (!tmp_minus)
> +		*out = tmp_plus;
> +	else
> +		*out = min(tmp_plus, tmp_minus);
> +
> +	char *end = *out + 1;
> +
> +	while (end < page_end) {
> +		if (!isalnum(*end) && *end != '*')
> +			break;
> +		end++;
> +	}
> +
> +	return end - *out;
> +}
> +EXPORT_SYMBOL_IF_KUNIT(vkms_configfs_parse_next_format);
> +
> +static ssize_t plane_supported_formats_store(struct config_item *item,
> +					     const char *page, size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +	int ret = 0;
> +	const char *end_page = page + count;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		while (1) {
> +			char *tmp;
> +			char fmt[4] = {' ', ' ', ' ', ' '};
> +			int len = vkms_configfs_parse_next_format(page, end_page, &tmp);
> +
> +			// No fourcc code found
> +			if (len <= 1 || len > 5)
> +				break;
> +
> +			page = tmp + len;
> +			memcpy(fmt, &tmp[1], min(len - 1, 4));
> +			if (tmp[0] == '+') {
> +				if (fmt[0] == '*') {
> +					ret = vkms_config_plane_add_all_formats(plane->config);
> +					if (ret)
> +						return ret;
> +				} else {
> +					ret = vkms_config_plane_add_format(plane->config,
> +									   *(int *)fmt);

I have been thinking for a while about this *(int *) casting and I'm not sure if it
would work in all cases.

I had a minor concern about int vs u32 and, while I don't think int will cause
issues, u32 looks like a better type.

My main concern was about endianess. The fourcc_code() macro shifts bits around,
which takes into account endianess. My brain hurt after trying to visualize this,
so I wrote a simple tests that works on x86_64 but fails on Power PC:

static void vkms_config_test_plane_add_format(struct kunit *test)
{
	struct vkms_config *config;
	struct vkms_config_plane *plane_cfg;
	int ret;
	u32 *formats;

	config = vkms_config_default_create(false, false, false, false);
	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, config);

	plane_cfg = get_first_plane(config);

	// DRM_FORMAT_XBGR16161616 = 942948952
	char fmt[4] = {'X', 'B', '4', '8'};

	vkms_config_plane_remove_all_formats(plane_cfg);
	ret = vkms_config_plane_get_supported_formats_count(plane_cfg);
	KUNIT_EXPECT_EQ(test, ret, 0);
	
	ret = vkms_config_plane_add_format(plane_cfg, *(int *)fmt);
	KUNIT_EXPECT_EQ(test, ret, 0);

	ret = vkms_config_plane_get_supported_formats_count(plane_cfg);
	KUNIT_EXPECT_EQ(test, ret, 1);

	formats = vkms_config_plane_get_supported_formats(plane_cfg);
	KUNIT_EXPECT_EQ(test, formats[0], DRM_FORMAT_XBGR16161616);
}

On big endian it fails with the following error:

[17:55:07] # vkms_config_test_plane_add_format: EXPECTATION FAILED at drivers/gpu/drm/vkms/tests/vkms_config_test.c:1256
[17:55:07] Expected ret == 0, but
[17:55:07]     ret == -22 (0xffffffffffffffea)
[17:55:07] # vkms_config_test_plane_add_format: EXPECTATION FAILED at drivers/gpu/drm/vkms/tests/vkms_config_test.c:1259
[17:55:07] Expected ret == 1, but
[17:55:07]     ret == 0 (0x0)
[17:55:07] # vkms_config_test_plane_add_format: EXPECTATION FAILED at drivers/gpu/drm/vkms/tests/vkms_config_test.c:1262
[17:55:07] Expected formats[0] == ((__u32)('X') | ((__u32)('B') << 8) | ((__u32)('4') << 16) | ((__u32)('8') << 24)), but
[17:55:07]     formats[0] == 875713089 (0x34325241)
[17:55:07]     ((__u32)('X') | ((__u32)('B') << 8) | ((__u32)('4') << 16) | ((__u32)('8') << 24)) == 942948952 (0x38344258)
[17:55:07] [FAILED] vkms_config_test_plane_add_format
[17:55:07]     # module: vkms_kunit_tests

So we need to find another way to convert the format. Maybe using the fourcc_code() macro?

Jose

> +					if (ret)
> +						return ret;
> +				}
> +			} else if (tmp[0] == '-') {
> +				if (fmt[0] == '*')
> +					vkms_config_plane_remove_all_formats(plane->config);
> +				else
> +					vkms_config_plane_remove_format(plane->config, *(int *)fmt);
> +			}
> +		}
> +	}
> +
> +	return count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
>  CONFIGFS_ATTR(plane_, name);
>  CONFIGFS_ATTR(plane_, supported_rotations);
> @@ -636,6 +752,7 @@ CONFIGFS_ATTR(plane_, supported_color_ranges);
>  CONFIGFS_ATTR(plane_, default_color_range);
>  CONFIGFS_ATTR(plane_, supported_color_encodings);
>  CONFIGFS_ATTR(plane_, default_color_encoding);
> +CONFIGFS_ATTR(plane_, supported_formats);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> @@ -646,6 +763,7 @@ static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_default_color_range,
>  	&plane_attr_supported_color_encodings,
>  	&plane_attr_default_color_encoding,
> +	&plane_attr_supported_formats,
>  	NULL,
>  };
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.h b/drivers/gpu/drm/vkms/vkms_configfs.h
> index e9020b0043db..2774655bfcc5 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.h
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.h
> @@ -2,7 +2,13 @@
>  #ifndef _VKMS_CONFIGFS_H_
>  #define _VKMS_CONFIGFS_H_
>  
> +#include <linux/types.h>
> +
>  int vkms_configfs_register(void);
>  void vkms_configfs_unregister(void);
>  
> +#if IS_ENABLED(CONFIG_KUNIT)
> +int vkms_configfs_parse_next_format(const char *page, const char *end_page, char **out);
> +#endif
> +
>  #endif /* _VKMS_CONFIGFS_H_ */
> 
> -- 
> 2.51.2
> 

On Mon, Dec 22, 2025 at 11:11:20AM +0100, Louis Chauvet wrote:
> To allow the userspace to test many hardware configuration, introduce a
> new interface to configure the available formats per planes. VKMS supports
> multiple formats, so the userspace can choose any combination.
> 
> The supported formats are configured by writing the fourcc code in
> supported_formats:
>  # enable AR24 format
>   echo '+AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable AR24 format
>   echo '-AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # enable all format supported by VKMS
>   echo '+*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable all formats
>   echo '-*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  Documentation/ABI/testing/configfs-vkms         |   9 ++
>  Documentation/gpu/vkms.rst                      |   7 +-
>  drivers/gpu/drm/vkms/tests/Makefile             |   3 +-
>  drivers/gpu/drm/vkms/tests/vkms_configfs_test.c | 102 ++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_configfs.c            | 118 ++++++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_configfs.h            |   6 ++
>  6 files changed, 243 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
> index 2ace79ce848a..48f92538c602 100644
> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -153,6 +153,15 @@ Description:
>          Default color range presented to userspace, same
>          values as supported_color_ranges.
>  
> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
> +Date:		Nov 2025
> +Contact:	dri-devel@lists.freedesktop.org
> +Description:
> +        List of supported formats for this plane. To add a new
> +        item, write its fourcc code prefixed with '+'. To remove,
> +        use '-' prefix. Use '+*' to add all formats, '-*' to
> +        remove all.
> +
>  What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>  Date:		Nov 2025
>  Contact:	dri-devel@lists.freedesktop.org
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index ab0eb2f97fc2..15d62ad963c9 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,7 +87,7 @@ Start by creating one or more planes::
>  
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>  
> -Planes have 8 configurable attributes:
> +Planes have 9 configurable attributes:
>  
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> @@ -109,6 +109,11 @@ Planes have 8 configurable attributes:
>    must be set too.
>  - default_color_range: Default color range presented to the userspace, same
>    values as supported_color_ranges
> +- supported_formats: List of supported formats for this plane. To add a new item in the
> +  list, write it using a plus and fourcc code: +XR24
> +  To remove a format, use a minus and its fourcc: -XR24
> +  To add all formats use +*
> +  To remove all formats, use -*
>  
>  Continue by creating one or more CRTCs::
>  
> diff --git a/drivers/gpu/drm/vkms/tests/Makefile b/drivers/gpu/drm/vkms/tests/Makefile
> index d4d9ba8d4c54..92cfa7262ba4 100644
> --- a/drivers/gpu/drm/vkms/tests/Makefile
> +++ b/drivers/gpu/drm/vkms/tests/Makefile
> @@ -3,6 +3,7 @@
>  vkms-kunit-tests-y := \
>  	vkms_config_test.o \
>  	vkms_format_test.o \
> -	vkms_color_test.o
> +	vkms_color_test.o \
> +	vkms_configfs_test.o \
>  
>  obj-$(CONFIG_DRM_VKMS_KUNIT_TEST) += vkms-kunit-tests.o
> diff --git a/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
> new file mode 100644
> index 000000000000..8d02c2c459d9
> --- /dev/null
> +++ b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include "linux/printk.h"
> +#include <kunit/test.h>
> +
> +#include "../vkms_configfs.h"
> +
> +MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
> +
> +/**
> + * struct vkms_configfs_parse_format_case - Store test case for format parsing
> + * @str: Contains the string to parse
> + * @str_len: str len
> + * @expected_len: expected len of the matched format
> + * @expected_offset: expected offset in the string for the parsed format
> + */
> +struct vkms_configfs_parse_format_case {
> +	const char *str;
> +	int str_len;
> +	int expected_len;
> +	int expected_offset;
> +};
> +
> +struct vkms_configfs_parse_format_case vkms_configfs_parse_format_test_cases[] = {
> +	{
> +		.str = "+RG24",
> +		.str_len = 6,
> +		.expected_len = 5,
> +		.expected_offset = 0,
> +	}, {
> +		.str = "-RG24",
> +		.str_len = 6,
> +		.expected_len = 5,
> +		.expected_offset = 0
> +	}, {
> +		.str = "  -RG24",
> +		.str_len = 8,
> +		.expected_len = 5,
> +		.expected_offset = 2
> +	}, {
> +		.str = "+*",
> +		.str_len = 3,
> +		.expected_len = 2,
> +		.expected_offset = 0
> +	}, {
> +		.str = "-RG24+RG24",
> +		.str_len = 11,
> +		.expected_len = 5,
> +		.expected_offset = 0
> +	}, {
> +		.str = "-R1+RG24",
> +		.str_len = 9,
> +		.expected_len = 3,
> +		.expected_offset = 0
> +	}, {
> +		.str = "\n-R1",
> +		.str_len = 5,
> +		.expected_len = 3,
> +		.expected_offset = 1
> +	}, {
> +		.str = "-R1111",
> +		.str_len = 3,
> +		.expected_len = 3,
> +		.expected_offset = 0
> +	}
> +};
> +
> +static void vkms_configfs_test_parse_format(struct kunit *test)
> +{
> +	const struct vkms_configfs_parse_format_case *param = test->param_value;
> +	char *out;
> +	int len = vkms_configfs_parse_next_format(param->str, param->str + param->str_len, &out);
> +
> +	KUNIT_EXPECT_EQ(test, len, param->expected_len);
> +	KUNIT_EXPECT_PTR_EQ(test, out, param->str + param->expected_offset);
> +}
> +
> +static void vkms_configfs_test_parse_format_get_desc(struct vkms_configfs_parse_format_case *t,
> +						     char *desc)
> +{
> +	snprintf(desc, KUNIT_PARAM_DESC_SIZE, "%s", t->str);
> +}
> +
> +KUNIT_ARRAY_PARAM(vkms_configfs_test_parse_format, vkms_configfs_parse_format_test_cases,
> +		  vkms_configfs_test_parse_format_get_desc
> +);
> +
> +static struct kunit_case vkms_configfs_test_cases[] = {
> +	KUNIT_CASE_PARAM(vkms_configfs_test_parse_format,
> +			 vkms_configfs_test_parse_format_gen_params),
> +	{}
> +};
> +
> +static struct kunit_suite vkms_configfs_test_suite = {
> +	.name = "vkms-configfs",
> +	.test_cases = vkms_configfs_test_cases,
> +};
> +
> +kunit_test_suite(vkms_configfs_test_suite);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Kunit test for vkms configfs utility");
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 7be6d10b2b68..a451d1122acf 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -3,6 +3,8 @@
>  #include <linux/configfs.h>
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
> +#include <linux/string.h>
> +#include <kunit/visibility.h>
>  
>  #include "vkms_drv.h"
>  #include "vkms_config.h"
> @@ -628,6 +630,120 @@ static ssize_t plane_default_color_encoding_store(struct config_item *item,
>  	return count;
>  }
>  
> +static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	page[0] = '\0';
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		u32 *formats = vkms_config_plane_get_supported_formats(plane->config);
> +
> +		for (int i = 0;
> +		     i < vkms_config_plane_get_supported_formats_count(plane->config);
> +		     i++) {
> +			char tmp[6] = { 0 };
> +			const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
> +					       (int)sizeof(*formats),
> +					       (char *)&formats[i]);
> +			if (ret < 0)
> +				return ret;
> +			/*
> +			 * Limitation of ConfigFS attributes, an attribute can't be bigger
> +			 * than PAGE_SIZE. This will crop the result if this plane support
> +			 * more than ≈1000 formats.
> +			 */
> +			if (ret + strlen(page) > PAGE_SIZE - 1)
> +				return -ENOMEM;
> +			strncat(page, tmp, ARRAY_SIZE(tmp));
> +		}
> +	}
> +
> +	return strlen(page);
> +}
> +
> +/**
> + * parse_next_format() - Parse the next format in page, skipping all non fourcc-related characters
> + * @page: page to search into
> + * @page_end: last character of the page
> + * @out: Output pointer, will point inside page
> + *
> + * Returns: size of the matched format, @out will point to the + or -
> + */
> +VISIBLE_IF_KUNIT
> +int vkms_configfs_parse_next_format(const char *page, const char *page_end, char **out)
> +{
> +	int count = page - page_end;

Shouldn't this be "page_end - page"? An example logging the variables shows
that "count" takes negative numbers:

$ echo "-XB48" | sudo tee /sys/kernel/config/vkms/gpu1/planes/plane0/supported_formats

[22854.585268] page = 000000001ec38388
[22854.585277] page_end = 000000000b71ccb5
[22854.585279] count = -6
[22854.585281] page = 00000000625917b4
[22854.585282] page_end = 000000000b71ccb5
[22854.585283] count = -1

Jose

> +	char *tmp_plus = strnchr(page, count, '+');
> +	char *tmp_minus = strnchr(page, count, '-');
> +
> +	if (!tmp_plus && !tmp_minus)
> +		return 0;
> +	if (!tmp_plus)
> +		*out = tmp_minus;
> +	else if (!tmp_minus)
> +		*out = tmp_plus;
> +	else
> +		*out = min(tmp_plus, tmp_minus);
> +
> +	char *end = *out + 1;
> +
> +	while (end < page_end) {
> +		if (!isalnum(*end) && *end != '*')
> +			break;
> +		end++;
> +	}
> +
> +	return end - *out;
> +}
> +EXPORT_SYMBOL_IF_KUNIT(vkms_configfs_parse_next_format);
> +
> +static ssize_t plane_supported_formats_store(struct config_item *item,
> +					     const char *page, size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +	int ret = 0;
> +	const char *end_page = page + count;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		while (1) {
> +			char *tmp;
> +			char fmt[4] = {' ', ' ', ' ', ' '};
> +			int len = vkms_configfs_parse_next_format(page, end_page, &tmp);
> +
> +			// No fourcc code found
> +			if (len <= 1 || len > 5)
> +				break;
> +
> +			page = tmp + len;
> +			memcpy(fmt, &tmp[1], min(len - 1, 4));
> +			if (tmp[0] == '+') {
> +				if (fmt[0] == '*') {
> +					ret = vkms_config_plane_add_all_formats(plane->config);
> +					if (ret)
> +						return ret;
> +				} else {
> +					ret = vkms_config_plane_add_format(plane->config,
> +									   *(int *)fmt);
> +					if (ret)
> +						return ret;
> +				}
> +			} else if (tmp[0] == '-') {
> +				if (fmt[0] == '*')
> +					vkms_config_plane_remove_all_formats(plane->config);
> +				else
> +					vkms_config_plane_remove_format(plane->config, *(int *)fmt);
> +			}
> +		}
> +	}
> +
> +	return count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
>  CONFIGFS_ATTR(plane_, name);
>  CONFIGFS_ATTR(plane_, supported_rotations);
> @@ -636,6 +752,7 @@ CONFIGFS_ATTR(plane_, supported_color_ranges);
>  CONFIGFS_ATTR(plane_, default_color_range);
>  CONFIGFS_ATTR(plane_, supported_color_encodings);
>  CONFIGFS_ATTR(plane_, default_color_encoding);
> +CONFIGFS_ATTR(plane_, supported_formats);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> @@ -646,6 +763,7 @@ static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_default_color_range,
>  	&plane_attr_supported_color_encodings,
>  	&plane_attr_default_color_encoding,
> +	&plane_attr_supported_formats,
>  	NULL,
>  };
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.h b/drivers/gpu/drm/vkms/vkms_configfs.h
> index e9020b0043db..2774655bfcc5 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.h
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.h
> @@ -2,7 +2,13 @@
>  #ifndef _VKMS_CONFIGFS_H_
>  #define _VKMS_CONFIGFS_H_
>  
> +#include <linux/types.h>
> +
>  int vkms_configfs_register(void);
>  void vkms_configfs_unregister(void);
>  
> +#if IS_ENABLED(CONFIG_KUNIT)
> +int vkms_configfs_parse_next_format(const char *page, const char *end_page, char **out);
> +#endif
> +
>  #endif /* _VKMS_CONFIGFS_H_ */
> 
> -- 
> 2.51.2
> 

On Mon, Dec 22, 2025 at 11:11:20AM +0100, Louis Chauvet wrote:
> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
> +Date:		Nov 2025
> +Contact:	dri-devel@lists.freedesktop.org
> +Description:
> +        List of supported formats for this plane. To add a new
> +        item, write its fourcc code prefixed with '+'. To remove,
> +        use '-' prefix. Use '+*' to add all formats, '-*' to
> +        remove all.
> +

Sphinx reports htmldocs warning:

Documentation/ABI/testing/configfs-vkms:199: WARNING: Inline emphasis start-string without end-string. [docutils]

I have to escape the wildcard:

---- >8 ----
diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
index a7fce35fcf91d1..3839b6e3c9c935 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -202,7 +202,7 @@ Contact:	dri-devel@lists.freedesktop.org
 Description:
         List of supported formats for this plane. To add a new
         item, write its fourcc code prefixed with '+'. To remove,
-        use '-' prefix. Use '+*' to add all formats, '-*' to
+        use '-' prefix. Use '+*' to add all formats, '-\*' to
         remove all.
 
 What:		/sys/kernel/config/vkms/<device>/planes/<plane>/zpos_enabled

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

On 12/25/25 01:59, Bagas Sanjaya wrote:
> On Mon, Dec 22, 2025 at 11:11:20AM +0100, Louis Chauvet wrote:
>> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
>> +Date:		Nov 2025
>> +Contact:	dri-devel@lists.freedesktop.org
>> +Description:
>> +        List of supported formats for this plane. To add a new
>> +        item, write its fourcc code prefixed with '+'. To remove,
>> +        use '-' prefix. Use '+*' to add all formats, '-*' to
>> +        remove all.
>> +
> 
> Sphinx reports htmldocs warning:
> 
> Documentation/ABI/testing/configfs-vkms:199: WARNING: Inline emphasis start-string without end-string. [docutils]
> 
> I have to escape the wildcard:
> 
> ---- >8 ----
> diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
> index a7fce35fcf91d1..3839b6e3c9c935 100644
> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -202,7 +202,7 @@ Contact:	dri-devel@lists.freedesktop.org
>   Description:
>           List of supported formats for this plane. To add a new
>           item, write its fourcc code prefixed with '+'. To remove,
> -        use '-' prefix. Use '+*' to add all formats, '-*' to
> +        use '-' prefix. Use '+*' to add all formats, '-\*' to

Hi, thanks for the fix!

I only have to escape the second wildcard? Not the `+*`?

>           remove all.
>   
>   What:		/sys/kernel/config/vkms/<device>/planes/<plane>/zpos_enabled
> 
> Thanks.
>

On Mon, Dec 29, 2025 at 04:33:47PM +0100, Louis Chauvet wrote:
> > @@ -202,7 +202,7 @@ Contact:	dri-devel@lists.freedesktop.org
> >   Description:
> >           List of supported formats for this plane. To add a new
> >           item, write its fourcc code prefixed with '+'. To remove,
> > -        use '-' prefix. Use '+*' to add all formats, '-*' to
> > +        use '-' prefix. Use '+*' to add all formats, '-\*' to
> 
> Hi, thanks for the fix!
> 
> I only have to escape the second wildcard? Not the `+*`?

Yup. Try make htmldocs without the patch and see.

-- 
An old man doll... just what I always wanted! - Clara

On Mon Dec 22, 2025 at 11:11 AM CET, Louis Chauvet wrote:
> To allow the userspace to test many hardware configuration, introduce a
> new interface to configure the available formats per planes. VKMS supports
> multiple formats, so the userspace can choose any combination.
>
> The supported formats are configured by writing the fourcc code in
> supported_formats:
>  # enable AR24 format
>   echo '+AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable AR24 format
>   echo '-AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # enable all format supported by VKMS
>   echo '+*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>  # disable all formats
>   echo '-*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -153,6 +153,15 @@ Description:
>          Default color range presented to userspace, same
>          values as supported_color_ranges.
>
> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
> +Date:		Nov 2025

Jan 2026.

> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,7 +87,7 @@ Start by creating one or more planes::
>
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 8 configurable attributes:
> +Planes have 9 configurable attributes:
>
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> @@ -109,6 +109,11 @@ Planes have 8 configurable attributes:
>    must be set too.
>  - default_color_range: Default color range presented to the userspace, same
>    values as supported_color_ranges
> +- supported_formats: List of supported formats for this plane. To add a new item in the
> +  list, write it using a plus and fourcc code: +XR24
> +  To remove a format, use a minus and its fourcc: -XR24

From the docs examples it's not obvious that you can add/remove multiple
formats in one write operation ("+XR24 -RG24"), but the implementation
allows it. So either add a more complete example or forbid multiple
operations in one write. I would consider the latter option seriously
because it would simplify the string parsing code, which is very tricky to
get right and robust.

> +++ b/drivers/gpu/drm/vkms/tests/vkms_configfs_test.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include "linux/printk.h"
> +#include <kunit/test.h>
> +
> +#include "../vkms_configfs.h"
> +
> +MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
> +
> +/**
> + * struct vkms_configfs_parse_format_case - Store test case for format parsing
> + * @str: Contains the string to parse
> + * @str_len: str len
> + * @expected_len: expected len of the matched format
> + * @expected_offset: expected offset in the string for the parsed format
> + */
> +struct vkms_configfs_parse_format_case {
> +	const char *str;
> +	int str_len;
> +	int expected_len;
> +	int expected_offset;
> +};
> +
> +struct vkms_configfs_parse_format_case vkms_configfs_parse_format_test_cases[] = {
> +	{
> +		.str = "+RG24",
> +		.str_len = 6,
> +		.expected_len = 5,
> +		.expected_offset = 0,

Thanks for having renamed 'data' to 'str'! However now I realize the
'str_len' name becomes misleading: the string length does not include the
training NUL character, while the value you need here does. I beg your
pardon... I guess 'str_len' should be renamed too, maybe to 'str_size' if
no better name comes to mind.

> +	}, {

Based on the question I asked after v3,resend and on your answer, I'd add a
clarifying comment here about the following test:

	   /* ensure the algorithm stops at data_len and not \0 */

> +		.str = "-R1111",
> +		.str_len = 3,
> +		.expected_len = 3,
> +		.expected_offset = 0
> +	}

Testing wrong and corner cases is more important than testing perfectly
clean cases. So it would be nice to add tests for not-obviously-wrong and
definitely-wrong cases, such as "+ RG24" (note the space), "fubar", "+**",
"*+", "++", "-+", "-A*42" (see below), ":-)" (dash after non-blank char)
and "(-o-)".

> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -3,6 +3,8 @@
>  #include <linux/configfs.h>
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
> +#include <linux/string.h>
> +#include <kunit/visibility.h>
>
>  #include "vkms_drv.h"
>  #include "vkms_config.h"
> @@ -628,6 +630,120 @@ static ssize_t plane_default_color_encoding_store(struct config_item *item,
>  	return count;
>  }
>
> +static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	page[0] = '\0';
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		u32 *formats = vkms_config_plane_get_supported_formats(plane->config);
> +
> +		for (int i = 0;
> +		     i < vkms_config_plane_get_supported_formats_count(plane->config);
> +		     i++) {
> +			char tmp[6] = { 0 };
> +			const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
> +					       (int)sizeof(*formats),
> +					       (char *)&formats[i]);
> +			if (ret < 0)
> +				return ret;
> +			/*
> +			 * Limitation of ConfigFS attributes, an attribute can't be bigger
> +			 * than PAGE_SIZE. This will crop the result if this plane support
> +			 * more than ≈1000 formats.

Every format takes 5 chars, so about 800 formats, no?

> +			 */
> +			if (ret + strlen(page) > PAGE_SIZE - 1)
> +				return -ENOMEM;
> +			strncat(page, tmp, ARRAY_SIZE(tmp));
> +		}
> +	}
> +
> +	return strlen(page);
> +}
> +
> +/**
> + * parse_next_format() - Parse the next format in page, skipping all non fourcc-related characters
> + * @page: page to search into
> + * @page_end: last character of the page
> + * @out: Output pointer, will point inside page
> + *
> + * Returns: size of the matched format, @out will point to the + or -
> + */
> +VISIBLE_IF_KUNIT
> +int vkms_configfs_parse_next_format(const char *page, const char *page_end, char **out)
> +{
> +	int count = page - page_end;
> +	char *tmp_plus = strnchr(page, count, '+');
> +	char *tmp_minus = strnchr(page, count, '-');
> +
> +	if (!tmp_plus && !tmp_minus)
> +		return 0;
> +	if (!tmp_plus)
> +		*out = tmp_minus;
> +	else if (!tmp_minus)
> +		*out = tmp_plus;
> +	else
> +		*out = min(tmp_plus, tmp_minus);
> +
> +	char *end = *out + 1;
> +
> +	while (end < page_end) {
> +		if (!isalnum(*end) && *end != '*')
> +			break;
> +		end++;
> +	}

I think this while loop will capture a string like "A*42", which is wrong.

Maybe you could change this function to be both stricter and simpler by not
trying to accept leading spaces, for example.

> +static ssize_t plane_supported_formats_store(struct config_item *item,
> +					     const char *page, size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +	int ret = 0;
> +	const char *end_page = page + count;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		while (1) {
> +			char *tmp;
> +			char fmt[4] = {' ', ' ', ' ', ' '};
> +			int len = vkms_configfs_parse_next_format(page, end_page, &tmp);
> +
> +			// No fourcc code found
> +			if (len <= 1 || len > 5)
> +				break;
> +
> +			page = tmp + len;
> +			memcpy(fmt, &tmp[1], min(len - 1, 4));
> +			if (tmp[0] == '+') {
> +				if (fmt[0] == '*') {
> +					ret = vkms_config_plane_add_all_formats(plane->config);
> +					if (ret)
> +						return ret;
> +				} else {
> +					ret = vkms_config_plane_add_format(plane->config,
> +									   *(int *)fmt);
> +					if (ret)
> +						return ret;
> +				}

Minor code simplification:

				if (fmt[0] == '*')
					ret = vkms_config_plane_add_all_formats(plane->config);
				else
					ret = vkms_config_plane_add_format(plane->config,
									   *(int *)fmt);
				if (ret)
					return ret;

Or, if you like the ternary operator:


				ret = (fmt[0] == '*') ?
					vkms_config_plane_add_all_formats(plane->config):
					vkms_config_plane_add_format(plane->config, *(int *)fmt);
				if (ret)
					return ret;

I'm sorry some of these comments could have been written asof v2, but this
patch is really intricate and they came to mind only while re-thinking
about the code.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Hi Louis,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8e7460eac786c72f48c4e04ce9be692b939428ce]

url:    https://github.com/intel-lab-lkp/linux/commits/Louis-Chauvet/Documentation-ABI-vkms-Add-current-VKMS-ABI-documentation/20251222-181426
base:   8e7460eac786c72f48c4e04ce9be692b939428ce
patch link:    https://lore.kernel.org/r/20251222-vkms-all-config-v3-18-ba42dc3fb9ff%40bootlin.com
patch subject: [PATCH v3 18/33] drm/vkms: Introduce configfs for plane format
reproduce: (https://download.01.org/0day-ci/archive/20251223/202512231419.lVidy4qV-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512231419.lVidy4qV-lkp@intel.com/

All warnings (new ones prefixed by >>):

   Using alabaster theme
   ERROR: Cannot find file ./include/linux/pci.h
   WARNING: No kernel-doc for file ./include/linux/pci.h
   ERROR: Cannot find file ./include/linux/mod_devicetable.h
   WARNING: No kernel-doc for file ./include/linux/mod_devicetable.h
>> Documentation/ABI/testing/configfs-vkms:156: WARNING: Inline emphasis start-string without end-string. [docutils]
   ERROR: Cannot find file ./include/linux/bootconfig.h
   WARNING: No kernel-doc for file ./include/linux/bootconfig.h
   ERROR: Cannot find file ./include/linux/pstore_zone.h
   ERROR: Cannot find file ./include/linux/pstore_zone.h
   WARNING: No kernel-doc for file ./include/linux/pstore_zone.h


vim +156 Documentation/ABI/testing/configfs-vkms

 > 156	What:		/sys/kernel/config/vkms/<device>/planes/<plane>/supported_formats
   157	Date:		Nov 2025
   158	Contact:	dri-devel@lists.freedesktop.org
   159	Description:
   160	        List of supported formats for this plane. To add a new
   161	        item, write its fourcc code prefixed with '+'. To remove,
   162	        use '-' prefix. Use '+*' to add all formats, '-*' to
   163	        remove all.
   164	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Louis,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8e7460eac786c72f48c4e04ce9be692b939428ce]

url:    https://github.com/intel-lab-lkp/linux/commits/Louis-Chauvet/Documentation-ABI-vkms-Add-current-VKMS-ABI-documentation/20251222-181426
base:   8e7460eac786c72f48c4e04ce9be692b939428ce
patch link:    https://lore.kernel.org/r/20251222-vkms-all-config-v3-18-ba42dc3fb9ff%40bootlin.com
patch subject: [PATCH v3 18/33] drm/vkms: Introduce configfs for plane format
config: i386-randconfig-141-20251223 (https://download.01.org/0day-ci/archive/20251223/202512230638.scAuFLVV-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251223/202512230638.scAuFLVV-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512230638.scAuFLVV-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Warning: drivers/gpu/drm/vkms/vkms_configfs.c:676 expecting prototype for parse_next_format(). Prototype was for vkms_configfs_parse_next_format() instead

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Louis,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8e7460eac786c72f48c4e04ce9be692b939428ce]

url:    https://github.com/intel-lab-lkp/linux/commits/Louis-Chauvet/Documentation-ABI-vkms-Add-current-VKMS-ABI-documentation/20251222-181426
base:   8e7460eac786c72f48c4e04ce9be692b939428ce
patch link:    https://lore.kernel.org/r/20251222-vkms-all-config-v3-18-ba42dc3fb9ff%40bootlin.com
patch subject: [PATCH v3 18/33] drm/vkms: Introduce configfs for plane format
config: x86_64-rhel-9.4 (https://download.01.org/0day-ci/archive/20251223/202512230158.yEDymogC-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251223/202512230158.yEDymogC-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512230158.yEDymogC-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Warning: drivers/gpu/drm/vkms/vkms_configfs.c:676 expecting prototype for parse_next_format(). Prototype was for vkms_configfs_parse_next_format() instead

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki