drm/amd/display: Initialise backlight level values from hw

Internal backlight levels are initialised from ACPI but the values
are sometimes out of sync with the levels in effect until there has
been a read from hardware (eg triggered by reading from sysfs).

This means that the first drm_commit can cause the levels to be set
to a different value than the actual starting one, which results in
a sudden change in brightness.

This path shows the problem (when the values are out of sync):

   amdgpu_dm_atomic_commit_tail()
   -> amdgpu_dm_commit_streams()
   -> amdgpu_dm_backlight_set_level(..., dm->brightness[n])

This patch calls the backlight ops get_brightness explicitly
at the end of backlight registration to make sure dm->brightness[n]
is in sync with the actual hardware levels.

Fixes: 2fe87f54abdc ("drm/amd/display: Set default brightness according to ACPI")
Signed-off-by: Vivek Das Mohapatra <vivek@collabora.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 318b1c36d82a0cd2b06a4bb43272fa6f1bc8adc1)
Cc: stable@vger.kernel.org

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 936c3bc3f2d607c8ba3be10f9ec93c93d3933075..fae88ce8327fa934638dc32ee39851ac019ed2ae 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5266,6 +5266,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
        struct amdgpu_dm_backlight_caps *caps;
        char bl_name[16];
        int min, max;
+       int real_brightness;
+       int init_brightness;
 
        if (aconnector->bl_idx == -1)
                return;
@@ -5290,6 +5292,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
        } else
                props.brightness = props.max_brightness = MAX_BACKLIGHT_LEVEL;
 
+       init_brightness = props.brightness;
+
        if (caps->data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE)) {
                drm_info(drm, "Using custom brightness curve\n");
                props.scale = BACKLIGHT_SCALE_NON_LINEAR;
@@ -5308,8 +5312,20 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
        if (IS_ERR(dm->backlight_dev[aconnector->bl_idx])) {
                drm_err(drm, "DM: Backlight registration failed!\n");
                dm->backlight_dev[aconnector->bl_idx] = NULL;
-       } else
+       } else {
+               /*
+                * dm->brightness[x] can be inconsistent just after startup until
+                * ops.get_brightness is called.
+                */
+               real_brightness =
+                       amdgpu_dm_backlight_ops.get_brightness(dm->backlight_dev[aconnector->bl_idx]);
+
+               if (real_brightness != init_brightness) {
+                       dm->actual_brightness[aconnector->bl_idx] = real_brightness;
+                       dm->brightness[aconnector->bl_idx] = real_brightness;
+               }
                drm_dbg_driver(drm, "DM: Registered Backlight device: %s\n", bl_name);
+       }
 }
 
 static int initialize_plane(struct amdgpu_display_manager *dm,