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

[Harry Wentland <harry.wentland@amd.com>]

On 2024-08-26 12:57, Mario Limonciello wrote:
> 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?).

How much darker? Is it bothersome?

I wonder the FW and driver have different min backlight values now.

Leo, any thoughts?

Harry

> 
>>
>> 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(
>>
>