Modern compositor rely on zpos managment to offload some processing to
deticated hardware. In order to test multiple configurations, add zpos
configuration to configFS.

Introduce multiple attributes to configure zpos:
- zpos_enabled - Create or not the zpos property. If not created, the zpos
  is undefined.
- zpos_mutable - If the zpos property is created, allow or not the
  userspace to modify it
- zpos_initial - Intial value for zpos property. Must be between zpos_min
  and zpos_max
- zpos_min - Minimal zpos value for this plane. Must be smaller than or
  equals to zpos_max
- zpos_max - Maximal zpos value for this plane. Must be greater than or
  equals to zpos_min

Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
---
 Documentation/gpu/vkms.rst           |   9 +-
 drivers/gpu/drm/vkms/vkms_configfs.c | 199 +++++++++++++++++++++++++++++++++++
 2 files changed, 207 insertions(+), 1 deletion(-)

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index deb14e7c48ea..d4ad4af45414 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 attribute:
+Planes have 13 configurable attribute:
 
 - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
   exposed by the "type" property of a plane)
@@ -111,6 +111,13 @@ Planes have 8 configurable attribute:
   To remove a format, use a minus and its fourcc: -XR24
   To add all formats use +*
   To remove all formats, use -*
+- zpos_enabled: Enable or not the zpos property: 1 enable, 0 disable
+- zpos_mutable: Create the zpos property as a mutable or imutable property: 1 mutable,
+  0 disable. No effect if zpos_enabled is not set.
+- zpos_initial: Set the initial zpos value. Must be between zpos_min and zpos_max. No
+  effect if zpos_enabled is not set.
+- zpos_min: Set the minimal zpos value. No effect if zpos_enabled is not set.
+- zpos_max: Set the maximal zpos value. No effect if zpos_enabled is not set.
 
 Continue by creating one or more CRTCs::
 
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 528f22fa2df1..fd1be7292058 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0+
+#include "asm-generic/errno-base.h"
 #include <linux/cleanup.h>
 #include <linux/configfs.h>
 #include <linux/mutex.h>
@@ -679,6 +680,194 @@ static ssize_t plane_supported_formats_store(struct config_item *item,
 	return count;
 }
 
+static ssize_t plane_zpos_enabled_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	bool enabled;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		enabled = vkms_config_plane_get_zpos_enabled(plane->config);
+
+	return sprintf(page, "%d\n", enabled);
+}
+
+static ssize_t plane_zpos_enabled_store(struct config_item *item, const char *page,
+					size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	bool enabled;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtobool(page, &enabled))
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		vkms_config_plane_set_zpos_enabled(plane->config, enabled);
+	}
+
+	return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_mutable_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	bool mutable;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		mutable = vkms_config_plane_get_zpos_mutable(plane->config);
+
+	return sprintf(page, "%d\n", mutable);
+}
+
+static ssize_t plane_zpos_mutable_store(struct config_item *item, const char *page,
+					size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	bool mutable;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtobool(page, &mutable))
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		vkms_config_plane_set_zpos_mutable(plane->config, mutable);
+	}
+
+	return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_initial_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int initial;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		initial = vkms_config_plane_get_zpos_initial(plane->config);
+
+	return sprintf(page, "%u\n", initial);
+}
+
+static ssize_t plane_zpos_initial_store(struct config_item *item, const char *page,
+					size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int initial;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtouint(page, 10, &initial))
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		if (initial > vkms_config_plane_get_zpos_max(plane->config))
+			return -EINVAL;
+
+		if (initial < vkms_config_plane_get_zpos_min(plane->config))
+			return -EINVAL;
+
+		vkms_config_plane_set_zpos_initial(plane->config, initial);
+	}
+
+	return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_min_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int min;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		min = vkms_config_plane_get_zpos_min(plane->config);
+
+	return sprintf(page, "%u\n", min);
+}
+
+static ssize_t plane_zpos_min_store(struct config_item *item, const char *page,
+				    size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int min;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtouint(page, 10, &min))
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		if (min > vkms_config_plane_get_zpos_max(plane->config))
+			return -EINVAL;
+
+		if (min > vkms_config_plane_get_zpos_initial(plane->config))
+			return -EINVAL;
+
+		vkms_config_plane_set_zpos_min(plane->config, min);
+	}
+
+	return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_max_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int max;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		max = vkms_config_plane_get_zpos_max(plane->config);
+
+	return sprintf(page, "%u\n", max);
+}
+
+static ssize_t plane_zpos_max_store(struct config_item *item, const char *page,
+				    size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	unsigned int max;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtouint(page, 10, &max))
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		if (max < vkms_config_plane_get_zpos_min(plane->config))
+			return -EINVAL;
+
+		if (max < vkms_config_plane_get_zpos_initial(plane->config))
+			return -EINVAL;
+
+		vkms_config_plane_set_zpos_max(plane->config, max);
+	}
+
+	return (ssize_t)count;
+}
+
 CONFIGFS_ATTR(plane_, type);
 CONFIGFS_ATTR(plane_, supported_rotations);
 CONFIGFS_ATTR(plane_, default_rotation);
@@ -687,6 +876,11 @@ CONFIGFS_ATTR(plane_, default_color_range);
 CONFIGFS_ATTR(plane_, supported_color_encoding);
 CONFIGFS_ATTR(plane_, default_color_encoding);
 CONFIGFS_ATTR(plane_, supported_formats);
+CONFIGFS_ATTR(plane_, zpos_enabled);
+CONFIGFS_ATTR(plane_, zpos_mutable);
+CONFIGFS_ATTR(plane_, zpos_initial);
+CONFIGFS_ATTR(plane_, zpos_min);
+CONFIGFS_ATTR(plane_, zpos_max);
 
 static struct configfs_attribute *plane_item_attrs[] = {
 	&plane_attr_type,
@@ -697,6 +891,11 @@ static struct configfs_attribute *plane_item_attrs[] = {
 	&plane_attr_supported_color_encoding,
 	&plane_attr_default_color_encoding,
 	&plane_attr_supported_formats,
+	&plane_attr_zpos_enabled,
+	&plane_attr_zpos_mutable,
+	&plane_attr_zpos_initial,
+	&plane_attr_zpos_min,
+	&plane_attr_zpos_max,
 	NULL,
 };
 

-- 
2.51.0

On Sat, Oct 18, 2025 at 04:01:13AM +0200, Louis Chauvet wrote:
> Modern compositor rely on zpos managment to offload some processing to
> deticated hardware. In order to test multiple configurations, add zpos
> configuration to configFS.
> 
> Introduce multiple attributes to configure zpos:
> - zpos_enabled - Create or not the zpos property. If not created, the zpos
>   is undefined.
> - zpos_mutable - If the zpos property is created, allow or not the
>   userspace to modify it
> - zpos_initial - Intial value for zpos property. Must be between zpos_min
>   and zpos_max
> - zpos_min - Minimal zpos value for this plane. Must be smaller than or
>   equals to zpos_max
> - zpos_max - Maximal zpos value for this plane. Must be greater than or
>   equals to zpos_min
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  Documentation/gpu/vkms.rst           |   9 +-
>  drivers/gpu/drm/vkms/vkms_configfs.c | 199 +++++++++++++++++++++++++++++++++++
>  2 files changed, 207 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index deb14e7c48ea..d4ad4af45414 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 attribute:
> +Planes have 13 configurable attribute:
>  
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> @@ -111,6 +111,13 @@ Planes have 8 configurable attribute:
>    To remove a format, use a minus and its fourcc: -XR24
>    To add all formats use +*
>    To remove all formats, use -*
> +- zpos_enabled: Enable or not the zpos property: 1 enable, 0 disable
> +- zpos_mutable: Create the zpos property as a mutable or imutable property: 1 mutable,
> +  0 disable. No effect if zpos_enabled is not set.
> +- zpos_initial: Set the initial zpos value. Must be between zpos_min and zpos_max. No
> +  effect if zpos_enabled is not set.
> +- zpos_min: Set the minimal zpos value. No effect if zpos_enabled is not set.
> +- zpos_max: Set the maximal zpos value. No effect if zpos_enabled is not set.

Aren't zpos_min/max also ignored when zpos_mutable is false?

>  Continue by creating one or more CRTCs::
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 528f22fa2df1..fd1be7292058 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -1,4 +1,5 @@
>  // SPDX-License-Identifier: GPL-2.0+
> +#include "asm-generic/errno-base.h"

Accidentally included by IDE?

>  #include <linux/cleanup.h>
>  #include <linux/configfs.h>
>  #include <linux/mutex.h>
> @@ -679,6 +680,194 @@ static ssize_t plane_supported_formats_store(struct config_item *item,
>  	return count;
>  }
>  
> +static ssize_t plane_zpos_enabled_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	bool enabled;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		enabled = vkms_config_plane_get_zpos_enabled(plane->config);
> +
> +	return sprintf(page, "%d\n", enabled);
> +}
> +
> +static ssize_t plane_zpos_enabled_store(struct config_item *item, const char *page,
> +					size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	bool enabled;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	if (kstrtobool(page, &enabled))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		vkms_config_plane_set_zpos_enabled(plane->config, enabled);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
> +static ssize_t plane_zpos_mutable_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	bool mutable;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		mutable = vkms_config_plane_get_zpos_mutable(plane->config);
> +
> +	return sprintf(page, "%d\n", mutable);
> +}
> +
> +static ssize_t plane_zpos_mutable_store(struct config_item *item, const char *page,
> +					size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	bool mutable;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	if (kstrtobool(page, &mutable))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		vkms_config_plane_set_zpos_mutable(plane->config, mutable);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
> +static ssize_t plane_zpos_initial_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int initial;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		initial = vkms_config_plane_get_zpos_initial(plane->config);
> +
> +	return sprintf(page, "%u\n", initial);
> +}
> +
> +static ssize_t plane_zpos_initial_store(struct config_item *item, const char *page,
> +					size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int initial;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	if (kstrtouint(page, 10, &initial))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		if (initial > vkms_config_plane_get_zpos_max(plane->config))
> +			return -EINVAL;
> +
> +		if (initial < vkms_config_plane_get_zpos_min(plane->config))
> +			return -EINVAL;
> +
> +		vkms_config_plane_set_zpos_initial(plane->config, initial);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
> +static ssize_t plane_zpos_min_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int min;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		min = vkms_config_plane_get_zpos_min(plane->config);
> +
> +	return sprintf(page, "%u\n", min);
> +}
> +
> +static ssize_t plane_zpos_min_store(struct config_item *item, const char *page,
> +				    size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int min;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	if (kstrtouint(page, 10, &min))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		if (min > vkms_config_plane_get_zpos_max(plane->config))
> +			return -EINVAL;
> +
> +		if (min > vkms_config_plane_get_zpos_initial(plane->config))
> +			return -EINVAL;
> +
> +		vkms_config_plane_set_zpos_min(plane->config, min);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
> +static ssize_t plane_zpos_max_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int max;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		max = vkms_config_plane_get_zpos_max(plane->config);
> +
> +	return sprintf(page, "%u\n", max);
> +}
> +
> +static ssize_t plane_zpos_max_store(struct config_item *item, const char *page,
> +				    size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int max;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	if (kstrtouint(page, 10, &max))
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		if (max < vkms_config_plane_get_zpos_min(plane->config))
> +			return -EINVAL;
> +
> +		if (max < vkms_config_plane_get_zpos_initial(plane->config))
> +			return -EINVAL;
> +
> +		vkms_config_plane_set_zpos_max(plane->config, max);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
>  CONFIGFS_ATTR(plane_, supported_rotations);
>  CONFIGFS_ATTR(plane_, default_rotation);
> @@ -687,6 +876,11 @@ CONFIGFS_ATTR(plane_, default_color_range);
>  CONFIGFS_ATTR(plane_, supported_color_encoding);
>  CONFIGFS_ATTR(plane_, default_color_encoding);
>  CONFIGFS_ATTR(plane_, supported_formats);
> +CONFIGFS_ATTR(plane_, zpos_enabled);
> +CONFIGFS_ATTR(plane_, zpos_mutable);
> +CONFIGFS_ATTR(plane_, zpos_initial);
> +CONFIGFS_ATTR(plane_, zpos_min);
> +CONFIGFS_ATTR(plane_, zpos_max);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> @@ -697,6 +891,11 @@ static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_supported_color_encoding,
>  	&plane_attr_default_color_encoding,
>  	&plane_attr_supported_formats,
> +	&plane_attr_zpos_enabled,
> +	&plane_attr_zpos_mutable,
> +	&plane_attr_zpos_initial,
> +	&plane_attr_zpos_min,
> +	&plane_attr_zpos_max,

LGTM, other than my previous comment on adding validation in this layer.
It can force to change attributtes in a specific order. I think we should
only validate in vkms_config_is_valid().

>  	NULL,
>  };
>  
> 
> -- 
> 2.51.0
>