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

[Alex Hung]

Reviewed-by: Alex Hung <alex.h...@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.limoncie...@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;