Commit 4aa8961b authored by Val Packett's avatar Val Packett Committed by Dmitry Baryshkov
Browse files

drm/dp: drm_edp_backlight_set_level: do not always send 3-byte commands 



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: f2db78e3 ("drm/dp: Modify drm_edp_backlight_set_level")
Signed-off-by: default avatarVal Packett <val@packett.cool>
Tested-by: default avatarAbel Vesa <abel.vesa@linaro.org>
Reviewed-by: default avatarSuraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20250706204446.8918-1-val@packett.cool


Signed-off-by: default avatarDmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
parent 043d9c69

drivers/gpu/drm/display/drm_dp_helper.c

+3 −1
Original line number Diff line number Diff line
@@ -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",