Re: [PATCH v6 2/4] drm/amd/display: Add support for minimum backlight quirk

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

On 8/24/2024 13:33, Thomas Weißschuh wrote:
> Not all platforms provide the full range of PWM backlight capabilities
> supported by the hardware through ATIF.
> Use the generic drm panel minimum backlight quirk infrastructure to
> override the capabilities where necessary.
> 
> Testing the backlight quirk together with the "panel_power_savings"
> sysfs file has not shown any negative impact.
> One quirk seems to be that 0% at panel_power_savings=0 seems to be
> slightly darker than at panel_power_savings=4.

Thanks; This is the kind of thing I was worried about.

Harry, Leo,

Is that expected?  I wonder if we need to internally turn off panel 
power savings in display code when brightness falls a threshold (12 IIRC 
was the real "minimum" advertised in the table?).

> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> Tested-by: Dustin L. Howett <dustin@howett.net>
> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/Kconfig                |  1 +
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++++++++
>   2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/Kconfig b/drivers/gpu/drm/amd/amdgpu/Kconfig
> index 0051fb1b437f..655c10aef2e3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/Kconfig
> +++ b/drivers/gpu/drm/amd/amdgpu/Kconfig
> @@ -23,6 +23,7 @@ config DRM_AMDGPU
>   	select DRM_BUDDY
>   	select DRM_SUBALLOC_HELPER
>   	select DRM_EXEC
> +	select DRM_PANEL_BACKLIGHT_QUIRKS
>   	# amdgpu depends on ACPI_VIDEO when ACPI is enabled, for select to work
>   	# ACPI_VIDEO's dependencies must also be selected.
>   	select INPUT if ACPI
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 983a977632ff..056960ea335c 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -93,6 +93,7 @@
>   #include <drm/drm_fourcc.h>
>   #include <drm/drm_edid.h>
>   #include <drm/drm_eld.h>
> +#include <drm/drm_utils.h>
>   #include <drm/drm_vblank.h>
>   #include <drm/drm_audio_component.h>
>   #include <drm/drm_gem_atomic_helper.h>
> @@ -3333,6 +3334,8 @@ static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
>   	struct drm_connector *conn_base;
>   	struct amdgpu_device *adev;
>   	struct drm_luminance_range_info *luminance_range;
> +	const struct drm_edid *drm_edid;
> +	int min_input_signal_override;
>   
>   	if (aconnector->bl_idx == -1 ||
>   	    aconnector->dc_link->connector_signal != SIGNAL_TYPE_EDP)
> @@ -3367,6 +3370,13 @@ static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
>   		caps->aux_min_input_signal = 0;
>   		caps->aux_max_input_signal = 512;
>   	}
> +
> +	drm_edid = drm_edid_alloc(aconnector->edid,
> +				  EDID_LENGTH * (aconnector->edid->extensions + 1));
> +	min_input_signal_override = drm_get_panel_min_brightness_quirk(drm_edid);
> +	drm_edid_free(drm_edid);
> +	if (min_input_signal_override >= 0)
> +		caps->min_input_signal = min_input_signal_override;
>   }
>   
>   void amdgpu_dm_update_connector_after_detect(
>