Panels using a PWM-controlled backlight source do not have a standard
way to communicate their valid PWM ranges.
On x86 the ranges are read from ACPI through driver-specific tables.
The built-in ranges are not necessarily correct, or may grow stale if an
older device can be retrofitted with newer panels.

Add a quirk infrastructure with which the minimum valid backlight value
can be maintained as part of the kernel.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Dustin L. Howett <dustin@howett.net>
---
 Documentation/gpu/drm-kms-helpers.rst        |  3 ++
 drivers/gpu/drm/Kconfig                      |  4 ++
 drivers/gpu/drm/Makefile                     |  1 +
 drivers/gpu/drm/drm_panel_backlight_quirks.c | 70 ++++++++++++++++++++++++++++
 include/drm/drm_utils.h                      |  4 ++
 5 files changed, 82 insertions(+)

diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index 8435e8621cc0..a26989500129 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -230,6 +230,9 @@ Panel Helper Reference
 .. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
    :export:
 
+.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
+   :export:
+
 Panel Self Refresh Helper Reference
 ===================================
 
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 6b2c6b91f962..9ebb8cdb535e 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -454,6 +454,10 @@ config DRM_HYPERV
 config DRM_EXPORT_FOR_TESTS
 	bool
 
+# Separate option as not all DRM drivers use it
+config DRM_PANEL_BACKLIGHT_QUIRKS
+	tristate
+
 config DRM_LIB_RANDOM
 	bool
 	default n
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 68cc9258ffc4..adf85999aee2 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -92,6 +92,7 @@ drm-$(CONFIG_DRM_PANIC) += drm_panic.o
 obj-$(CONFIG_DRM)	+= drm.o
 
 obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
+obj-$(CONFIG_DRM_PANEL_BACKLIGHT_QUIRKS) += drm_panel_backlight_quirks.o
 
 #
 # Memory-management helpers
diff --git a/drivers/gpu/drm/drm_panel_backlight_quirks.c b/drivers/gpu/drm/drm_panel_backlight_quirks.c
new file mode 100644
index 000000000000..6b8bbed77c7f
--- /dev/null
+++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/array_size.h>
+#include <linux/dmi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_utils.h>
+
+struct drm_panel_min_backlight_quirk {
+	struct {
+		enum dmi_field field;
+		const char * const value;
+	} dmi_match;
+	struct drm_edid_ident ident;
+	u8 min_brightness;
+};
+
+static const struct drm_panel_min_backlight_quirk drm_panel_min_backlight_quirks[] = {
+};
+
+static bool drm_panel_min_backlight_quirk_matches(const struct drm_panel_min_backlight_quirk *quirk,
+						  const struct drm_edid *edid)
+{
+	if (!dmi_match(quirk->dmi_match.field, quirk->dmi_match.value))
+		return false;
+
+	if (!drm_edid_match(edid, &quirk->ident))
+		return false;
+
+	return true;
+}
+
+/**
+ * drm_get_panel_min_brightness_quirk - Get minimum supported brightness level for a panel.
+ * @edid: EDID of the panel to check
+ *
+ * This function checks for platform specific (e.g. DMI based) quirks
+ * providing info on the minimum backlight brightness for systems where this
+ * cannot be probed correctly from the hard-/firm-ware.
+ *
+ * Returns:
+ * A negative error value or
+ * an override value in the range [0, 255] representing 0-100% to be scaled to
+ * the drivers target range.
+ */
+int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid)
+{
+	const struct drm_panel_min_backlight_quirk *quirk;
+	size_t i;
+
+	if (!IS_ENABLED(CONFIG_DMI))
+		return -ENODATA;
+
+	if (!edid)
+		return -EINVAL;
+
+	for (i = 0; i < ARRAY_SIZE(drm_panel_min_backlight_quirks); i++) {
+		quirk = &drm_panel_min_backlight_quirks[i];
+
+		if (drm_panel_min_backlight_quirk_matches(quirk, edid))
+			return quirk->min_brightness;
+	}
+
+	return -ENODATA;
+}
+EXPORT_SYMBOL(drm_get_panel_min_brightness_quirk);
+
+MODULE_DESCRIPTION("Quirks for panel backlight overrides");
+MODULE_LICENSE("GPL");
diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
index 70775748d243..15fa9b6865f4 100644
--- a/include/drm/drm_utils.h
+++ b/include/drm/drm_utils.h
@@ -12,8 +12,12 @@
 
 #include <linux/types.h>
 
+struct drm_edid;
+
 int drm_get_panel_orientation_quirk(int width, int height);
 
+int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid);
+
 signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
 
 #endif

-- 
2.46.0

On 8/18/2024 01:56, Thomas Weißschuh wrote:
> Panels using a PWM-controlled backlight source do not have a standard
> way to communicate their valid PWM ranges.
> On x86 the ranges are read from ACPI through driver-specific tables.
> The built-in ranges are not necessarily correct, or may grow stale if an
> older device can be retrofitted with newer panels.
> 
> Add a quirk infrastructure with which the minimum valid backlight value
> can be maintained as part of the kernel.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> Tested-by: Dustin L. Howett <dustin@howett.net>

One small nit below but otherwise this patch is fine to me.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>

> ---
>   Documentation/gpu/drm-kms-helpers.rst        |  3 ++
>   drivers/gpu/drm/Kconfig                      |  4 ++
>   drivers/gpu/drm/Makefile                     |  1 +
>   drivers/gpu/drm/drm_panel_backlight_quirks.c | 70 ++++++++++++++++++++++++++++
>   include/drm/drm_utils.h                      |  4 ++
>   5 files changed, 82 insertions(+)
> 
> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> index 8435e8621cc0..a26989500129 100644
> --- a/Documentation/gpu/drm-kms-helpers.rst
> +++ b/Documentation/gpu/drm-kms-helpers.rst
> @@ -230,6 +230,9 @@ Panel Helper Reference
>   .. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
>      :export:
>   
> +.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
> +   :export:
> +
>   Panel Self Refresh Helper Reference
>   ===================================
>   
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 6b2c6b91f962..9ebb8cdb535e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -454,6 +454,10 @@ config DRM_HYPERV
>   config DRM_EXPORT_FOR_TESTS
>   	bool
>   
> +# Separate option as not all DRM drivers use it
> +config DRM_PANEL_BACKLIGHT_QUIRKS
> +	tristate
> +
>   config DRM_LIB_RANDOM
>   	bool
>   	default n
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 68cc9258ffc4..adf85999aee2 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -92,6 +92,7 @@ drm-$(CONFIG_DRM_PANIC) += drm_panic.o
>   obj-$(CONFIG_DRM)	+= drm.o
>   
>   obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
> +obj-$(CONFIG_DRM_PANEL_BACKLIGHT_QUIRKS) += drm_panel_backlight_quirks.o
>   
>   #
>   # Memory-management helpers
> diff --git a/drivers/gpu/drm/drm_panel_backlight_quirks.c b/drivers/gpu/drm/drm_panel_backlight_quirks.c
> new file mode 100644
> index 000000000000..6b8bbed77c7f
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
> @@ -0,0 +1,70 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/array_size.h>
> +#include <linux/dmi.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <drm/drm_edid.h>
> +#include <drm/drm_utils.h>
> +
> +struct drm_panel_min_backlight_quirk {
> +	struct {
> +		enum dmi_field field;
> +		const char * const value;
> +	} dmi_match;
> +	struct drm_edid_ident ident;
> +	u8 min_brightness;
> +};
> +
> +static const struct drm_panel_min_backlight_quirk drm_panel_min_backlight_quirks[] = {
> +};
> +
> +static bool drm_panel_min_backlight_quirk_matches(const struct drm_panel_min_backlight_quirk *quirk,
> +						  const struct drm_edid *edid)
> +{
> +	if (!dmi_match(quirk->dmi_match.field, quirk->dmi_match.value))
> +		return false;
> +
> +	if (!drm_edid_match(edid, &quirk->ident))
> +		return false;
> +
> +	return true;
> +}
> +
> +/**
> + * drm_get_panel_min_brightness_quirk - Get minimum supported brightness level for a panel.
> + * @edid: EDID of the panel to check
> + *
> + * This function checks for platform specific (e.g. DMI based) quirks
> + * providing info on the minimum backlight brightness for systems where this
> + * cannot be probed correctly from the hard-/firm-ware.
> + *
> + * Returns:
> + * A negative error value or
> + * an override value in the range [0, 255] representing 0-100% to be scaled to
> + * the drivers target range.
> + */
> +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid)
> +{
> +	const struct drm_panel_min_backlight_quirk *quirk;
> +	size_t i;

Nit: this doesn't really seem like it needs to be size_t.  Shouldn't it 
just be an unsigned int?

> +
> +	if (!IS_ENABLED(CONFIG_DMI))
> +		return -ENODATA;
> +
> +	if (!edid)
> +		return -EINVAL;
> +
> +	for (i = 0; i < ARRAY_SIZE(drm_panel_min_backlight_quirks); i++) {
> +		quirk = &drm_panel_min_backlight_quirks[i];
> +
> +		if (drm_panel_min_backlight_quirk_matches(quirk, edid))
> +			return quirk->min_brightness;
> +	}
> +
> +	return -ENODATA;
> +}
> +EXPORT_SYMBOL(drm_get_panel_min_brightness_quirk);
> +
> +MODULE_DESCRIPTION("Quirks for panel backlight overrides");
> +MODULE_LICENSE("GPL");
> diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
> index 70775748d243..15fa9b6865f4 100644
> --- a/include/drm/drm_utils.h
> +++ b/include/drm/drm_utils.h
> @@ -12,8 +12,12 @@
>   
>   #include <linux/types.h>
>   
> +struct drm_edid;
> +
>   int drm_get_panel_orientation_quirk(int width, int height);
>   
> +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid);
> +
>   signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
>   
>   #endif
> 

On 2024-08-21 15:51:17+0000, Mario Limonciello wrote:
> On 8/18/2024 01:56, Thomas Weißschuh wrote:
> > Panels using a PWM-controlled backlight source do not have a standard
> > way to communicate their valid PWM ranges.
> > On x86 the ranges are read from ACPI through driver-specific tables.
> > The built-in ranges are not necessarily correct, or may grow stale if an
> > older device can be retrofitted with newer panels.
> > 
> > Add a quirk infrastructure with which the minimum valid backlight value
> > can be maintained as part of the kernel.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > Tested-by: Dustin L. Howett <dustin@howett.net>
> 
> One small nit below but otherwise this patch is fine to me.
> 
> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
> 
> > ---
> >   Documentation/gpu/drm-kms-helpers.rst        |  3 ++
> >   drivers/gpu/drm/Kconfig                      |  4 ++
> >   drivers/gpu/drm/Makefile                     |  1 +
> >   drivers/gpu/drm/drm_panel_backlight_quirks.c | 70 ++++++++++++++++++++++++++++
> >   include/drm/drm_utils.h                      |  4 ++
> >   5 files changed, 82 insertions(+)
> > 
> > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> > index 8435e8621cc0..a26989500129 100644
> > --- a/Documentation/gpu/drm-kms-helpers.rst
> > +++ b/Documentation/gpu/drm-kms-helpers.rst
> > @@ -230,6 +230,9 @@ Panel Helper Reference
> >   .. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
> >      :export:
> > +.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
> > +   :export:
> > +
> >   Panel Self Refresh Helper Reference
> >   ===================================
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index 6b2c6b91f962..9ebb8cdb535e 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -454,6 +454,10 @@ config DRM_HYPERV
> >   config DRM_EXPORT_FOR_TESTS
> >   	bool
> > +# Separate option as not all DRM drivers use it
> > +config DRM_PANEL_BACKLIGHT_QUIRKS
> > +	tristate
> > +
> >   config DRM_LIB_RANDOM
> >   	bool
> >   	default n
> > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> > index 68cc9258ffc4..adf85999aee2 100644
> > --- a/drivers/gpu/drm/Makefile
> > +++ b/drivers/gpu/drm/Makefile
> > @@ -92,6 +92,7 @@ drm-$(CONFIG_DRM_PANIC) += drm_panic.o
> >   obj-$(CONFIG_DRM)	+= drm.o
> >   obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
> > +obj-$(CONFIG_DRM_PANEL_BACKLIGHT_QUIRKS) += drm_panel_backlight_quirks.o
> >   #
> >   # Memory-management helpers
> > diff --git a/drivers/gpu/drm/drm_panel_backlight_quirks.c b/drivers/gpu/drm/drm_panel_backlight_quirks.c
> > new file mode 100644
> > index 000000000000..6b8bbed77c7f
> > --- /dev/null
> > +++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
> > @@ -0,0 +1,70 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/array_size.h>
> > +#include <linux/dmi.h>
> > +#include <linux/mod_devicetable.h>
> > +#include <linux/module.h>
> > +#include <drm/drm_edid.h>
> > +#include <drm/drm_utils.h>
> > +
> > +struct drm_panel_min_backlight_quirk {
> > +	struct {
> > +		enum dmi_field field;
> > +		const char * const value;
> > +	} dmi_match;
> > +	struct drm_edid_ident ident;
> > +	u8 min_brightness;
> > +};
> > +
> > +static const struct drm_panel_min_backlight_quirk drm_panel_min_backlight_quirks[] = {
> > +};
> > +
> > +static bool drm_panel_min_backlight_quirk_matches(const struct drm_panel_min_backlight_quirk *quirk,
> > +						  const struct drm_edid *edid)
> > +{
> > +	if (!dmi_match(quirk->dmi_match.field, quirk->dmi_match.value))
> > +		return false;
> > +
> > +	if (!drm_edid_match(edid, &quirk->ident))
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> > +/**
> > + * drm_get_panel_min_brightness_quirk - Get minimum supported brightness level for a panel.
> > + * @edid: EDID of the panel to check
> > + *
> > + * This function checks for platform specific (e.g. DMI based) quirks
> > + * providing info on the minimum backlight brightness for systems where this
> > + * cannot be probed correctly from the hard-/firm-ware.
> > + *
> > + * Returns:
> > + * A negative error value or
> > + * an override value in the range [0, 255] representing 0-100% to be scaled to
> > + * the drivers target range.
> > + */
> > +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid)
> > +{
> > +	const struct drm_panel_min_backlight_quirk *quirk;
> > +	size_t i;
> 
> Nit: this doesn't really seem like it needs to be size_t.  Shouldn't it just
> be an unsigned int?

ARRAY_SIZE() works with sizeof() which returns size_t.
It doesn't really matter, but I slightly prefer to keep the size_t.

> > +
> > +	if (!IS_ENABLED(CONFIG_DMI))
> > +		return -ENODATA;
> > +
> > +	if (!edid)
> > +		return -EINVAL;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(drm_panel_min_backlight_quirks); i++) {
> > +		quirk = &drm_panel_min_backlight_quirks[i];
> > +
> > +		if (drm_panel_min_backlight_quirk_matches(quirk, edid))
> > +			return quirk->min_brightness;
> > +	}
> > +
> > +	return -ENODATA;
> > +}
> > +EXPORT_SYMBOL(drm_get_panel_min_brightness_quirk);
> > +
> > +MODULE_DESCRIPTION("Quirks for panel backlight overrides");
> > +MODULE_LICENSE("GPL");
> > diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
> > index 70775748d243..15fa9b6865f4 100644
> > --- a/include/drm/drm_utils.h
> > +++ b/include/drm/drm_utils.h
> > @@ -12,8 +12,12 @@
> >   #include <linux/types.h>
> > +struct drm_edid;
> > +
> >   int drm_get_panel_orientation_quirk(int width, int height);
> > +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid);
> > +
> >   signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
> >   #endif
> > 
> 

On 8/22/2024 01:12, Thomas Weißschuh wrote:
> On 2024-08-21 15:51:17+0000, Mario Limonciello wrote:
>> On 8/18/2024 01:56, Thomas Weißschuh wrote:
>>> Panels using a PWM-controlled backlight source do not have a standard
>>> way to communicate their valid PWM ranges.
>>> On x86 the ranges are read from ACPI through driver-specific tables.
>>> The built-in ranges are not necessarily correct, or may grow stale if an
>>> older device can be retrofitted with newer panels.
>>>
>>> Add a quirk infrastructure with which the minimum valid backlight value
>>> can be maintained as part of the kernel.
>>>
>>> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
>>> Tested-by: Dustin L. Howett <dustin@howett.net>
>>
>> One small nit below but otherwise this patch is fine to me.
>>
>> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
>>
>>> ---
>>>    Documentation/gpu/drm-kms-helpers.rst        |  3 ++
>>>    drivers/gpu/drm/Kconfig                      |  4 ++
>>>    drivers/gpu/drm/Makefile                     |  1 +
>>>    drivers/gpu/drm/drm_panel_backlight_quirks.c | 70 ++++++++++++++++++++++++++++
>>>    include/drm/drm_utils.h                      |  4 ++
>>>    5 files changed, 82 insertions(+)
>>>
>>> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
>>> index 8435e8621cc0..a26989500129 100644
>>> --- a/Documentation/gpu/drm-kms-helpers.rst
>>> +++ b/Documentation/gpu/drm-kms-helpers.rst
>>> @@ -230,6 +230,9 @@ Panel Helper Reference
>>>    .. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
>>>       :export:
>>> +.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
>>> +   :export:
>>> +
>>>    Panel Self Refresh Helper Reference
>>>    ===================================
>>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>>> index 6b2c6b91f962..9ebb8cdb535e 100644
>>> --- a/drivers/gpu/drm/Kconfig
>>> +++ b/drivers/gpu/drm/Kconfig
>>> @@ -454,6 +454,10 @@ config DRM_HYPERV
>>>    config DRM_EXPORT_FOR_TESTS
>>>    	bool
>>> +# Separate option as not all DRM drivers use it
>>> +config DRM_PANEL_BACKLIGHT_QUIRKS
>>> +	tristate
>>> +
>>>    config DRM_LIB_RANDOM
>>>    	bool
>>>    	default n
>>> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
>>> index 68cc9258ffc4..adf85999aee2 100644
>>> --- a/drivers/gpu/drm/Makefile
>>> +++ b/drivers/gpu/drm/Makefile
>>> @@ -92,6 +92,7 @@ drm-$(CONFIG_DRM_PANIC) += drm_panic.o
>>>    obj-$(CONFIG_DRM)	+= drm.o
>>>    obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
>>> +obj-$(CONFIG_DRM_PANEL_BACKLIGHT_QUIRKS) += drm_panel_backlight_quirks.o
>>>    #
>>>    # Memory-management helpers
>>> diff --git a/drivers/gpu/drm/drm_panel_backlight_quirks.c b/drivers/gpu/drm/drm_panel_backlight_quirks.c
>>> new file mode 100644
>>> index 000000000000..6b8bbed77c7f
>>> --- /dev/null
>>> +++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
>>> @@ -0,0 +1,70 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#include <linux/array_size.h>
>>> +#include <linux/dmi.h>
>>> +#include <linux/mod_devicetable.h>
>>> +#include <linux/module.h>
>>> +#include <drm/drm_edid.h>
>>> +#include <drm/drm_utils.h>
>>> +
>>> +struct drm_panel_min_backlight_quirk {
>>> +	struct {
>>> +		enum dmi_field field;
>>> +		const char * const value;
>>> +	} dmi_match;
>>> +	struct drm_edid_ident ident;
>>> +	u8 min_brightness;
>>> +};
>>> +
>>> +static const struct drm_panel_min_backlight_quirk drm_panel_min_backlight_quirks[] = {
>>> +};
>>> +
>>> +static bool drm_panel_min_backlight_quirk_matches(const struct drm_panel_min_backlight_quirk *quirk,
>>> +						  const struct drm_edid *edid)
>>> +{
>>> +	if (!dmi_match(quirk->dmi_match.field, quirk->dmi_match.value))
>>> +		return false;
>>> +
>>> +	if (!drm_edid_match(edid, &quirk->ident))
>>> +		return false;
>>> +
>>> +	return true;
>>> +}
>>> +
>>> +/**
>>> + * drm_get_panel_min_brightness_quirk - Get minimum supported brightness level for a panel.
>>> + * @edid: EDID of the panel to check
>>> + *
>>> + * This function checks for platform specific (e.g. DMI based) quirks
>>> + * providing info on the minimum backlight brightness for systems where this
>>> + * cannot be probed correctly from the hard-/firm-ware.
>>> + *
>>> + * Returns:
>>> + * A negative error value or
>>> + * an override value in the range [0, 255] representing 0-100% to be scaled to
>>> + * the drivers target range.
>>> + */
>>> +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid)
>>> +{
>>> +	const struct drm_panel_min_backlight_quirk *quirk;
>>> +	size_t i;
>>
>> Nit: this doesn't really seem like it needs to be size_t.  Shouldn't it just
>> be an unsigned int?
> 
> ARRAY_SIZE() works with sizeof() which returns size_t.
> It doesn't really matter, but I slightly prefer to keep the size_t.

Ah thanks, I didn't realize that.  Feel free to leave as is then.

> 
>>> +
>>> +	if (!IS_ENABLED(CONFIG_DMI))
>>> +		return -ENODATA;
>>> +
>>> +	if (!edid)
>>> +		return -EINVAL;
>>> +
>>> +	for (i = 0; i < ARRAY_SIZE(drm_panel_min_backlight_quirks); i++) {
>>> +		quirk = &drm_panel_min_backlight_quirks[i];
>>> +
>>> +		if (drm_panel_min_backlight_quirk_matches(quirk, edid))
>>> +			return quirk->min_brightness;
>>> +	}
>>> +
>>> +	return -ENODATA;
>>> +}
>>> +EXPORT_SYMBOL(drm_get_panel_min_brightness_quirk);
>>> +
>>> +MODULE_DESCRIPTION("Quirks for panel backlight overrides");
>>> +MODULE_LICENSE("GPL");
>>> diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
>>> index 70775748d243..15fa9b6865f4 100644
>>> --- a/include/drm/drm_utils.h
>>> +++ b/include/drm/drm_utils.h
>>> @@ -12,8 +12,12 @@
>>>    #include <linux/types.h>
>>> +struct drm_edid;
>>> +
>>>    int drm_get_panel_orientation_quirk(int width, int height);
>>> +int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid);
>>> +
>>>    signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
>>>    #endif
>>>
>>