6.17-stable review patch. If anyone has any objections, please let me know.
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From: Val Packett val@packett.cool
[ Upstream commit 4aa8961b1b9c7498550b41168a91cf1558133dd3 ]
At least some panels using the LSB register are not happy with the unconditional increase of the command buffer to 3 bytes.
With the BOE NE14QDM in my Dell Latitude 7455, the recent patches for luminance based brightness have introduced a regression: the brightness range stopped being contiguous and became nonsensical (it probably was interpreting the last 2 bytes of the buffer and not the first 2).
Change from using a fixed sizeof() to a length variable that's only set to 3 when luminance is used. Let's leave the default as 2 even for the single-byte version, since that's how it worked before.
Fixes: f2db78e37fe7 ("drm/dp: Modify drm_edp_backlight_set_level") Signed-off-by: Val Packett val@packett.cool Tested-by: Abel Vesa abel.vesa@linaro.org Reviewed-by: Suraj Kandpal suraj.kandpal@intel.com Link: https://lore.kernel.org/r/20250706204446.8918-1-val@packett.cool Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@oss.qualcomm.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/display/drm_dp_helper.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c index 1ecc3df7e3167..4aaeae4fa03c3 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -3962,6 +3962,7 @@ int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_bac int ret; unsigned int offset = DP_EDP_BACKLIGHT_BRIGHTNESS_MSB; u8 buf[3] = { 0 }; + size_t len = 2;
/* The panel uses the PWM for controlling brightness levels */ if (!(bl->aux_set || bl->luminance_set)) @@ -3974,6 +3975,7 @@ int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_bac buf[1] = (level & 0x00ff00) >> 8; buf[2] = (level & 0xff0000) >> 16; offset = DP_EDP_PANEL_TARGET_LUMINANCE_VALUE; + len = 3; } else if (bl->lsb_reg_used) { buf[0] = (level & 0xff00) >> 8; buf[1] = (level & 0x00ff); @@ -3981,7 +3983,7 @@ int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_bac buf[0] = level; }
- ret = drm_dp_dpcd_write_data(aux, offset, buf, sizeof(buf)); + ret = drm_dp_dpcd_write_data(aux, offset, buf, len); if (ret < 0) { drm_err(aux->drm_dev, "%s: Failed to write aux backlight level: %d\n",