Re: [PATCH v5 1/4] drm: Add panel backlight quirks

[Mario Limonciello <mario.limonciello@amd.com>]

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
>