[PATCH v2 5/5] drm/amd/display: Add a new dcdebugmask to allow turning off brightness curve

[Alex Hung]

Reviewed-by: Alex Hung <alex.hung at amd.com>

On 2/28/25 11:51, Mario Limonciello wrote:
> Upgrading the kernel may cause some systems that were previously not using
> a firmware specified brightness curve to use one.
> 
> In the event of problems with this curve (for example an interpolation
> error) add a new dcdebugmask value that can be used to turn it off.  Also
> add an info message to show that custom brightness curves are currently in
> use.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
> ---
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 +++++
>   drivers/gpu/drm/amd/include/amd_shared.h          | 4 ++++
>   2 files changed, 9 insertions(+)
> 
> 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 b252c67f2bc4..63b66e2c9ab9 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -4767,6 +4767,9 @@ static u32 convert_brightness_from_user(const struct amdgpu_dm_backlight_caps *c
>   	for (int i = 0; i < caps->data_points; i++) {
>   		u8 signal, lum;
>   
> +		if (amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE)
> +			break;
> +
>   		signal = caps->luminance_data[i].input_signal;
>   		lum = caps->luminance_data[i].luminance;
>   
> @@ -4951,6 +4954,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
>   	} else
>   		props.brightness = AMDGPU_MAX_BL_LEVEL;
>   
> +	if (caps.data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE))
> +		drm_info(drm, "Using custom brightness curve\n");
>   	props.max_brightness = AMDGPU_MAX_BL_LEVEL;
>   	props.type = BACKLIGHT_RAW;
>   
> diff --git a/drivers/gpu/drm/amd/include/amd_shared.h b/drivers/gpu/drm/amd/include/amd_shared.h
> index c0538763ec1a..485b713cfad0 100644
> --- a/drivers/gpu/drm/amd/include/amd_shared.h
> +++ b/drivers/gpu/drm/amd/include/amd_shared.h
> @@ -354,6 +354,10 @@ enum DC_DEBUG_MASK {
>   	 * @DC_DISABLE_SUBVP: If set, disable DCN Sub-Viewport feature in amdgpu driver.
>   	 */
>   	DC_DISABLE_SUBVP = 0x20000,
> +	/**
> +	 * @DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE: If set, disable support for custom brightness curves
> +	 */
> +	DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE = 0x40000,
>   };
>   
>   enum amd_dpm_forced_level;