Commit 0fb03890 authored by Suraj Kandpal's avatar Suraj Kandpal
Browse files

drm/i915/backlight: Check if VESA backlight is possible 

Check if BACKLIGHT_BRIGHTNESS_AUX_SET_CAPABLE bit is
set then EDP_PWMGEN_BIT_COUNT_CAP_MIN and EDP_PWMGEN_BIT_COUNT_CAP_MAX
follow the eDP 1.4b Section 10.3. Which states min should
be >= 1 and max should be >= min. Some legacy panels
do not follow this properly. They set the
BACKLIGHT_BRIGHTNESS_AUX_SET_CAPABLE bit while not correctly
populating the min and max fields leading to a 0 max value.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7514


Fixes: 40d2f582 ("drm/i915/backlight: Remove try_vesa_interface")
Signed-off-by: default avatarSuraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: default avatarPranay Samala <pranay.samala@intel.com>
Link: https://patch.msgid.link/20260316031850.81794-1-suraj.kandpal@intel.com
parent 3ccc8a92

drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

+31 −1
Original line number Diff line number Diff line
@@ -609,6 +609,34 @@ static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, 
	return 0;

}



static bool

check_if_vesa_backlight_possible(struct intel_dp *intel_dp)

{

	int ret;

	u8 bit_min, bit_max;



	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))

		return true;



	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);

	if (ret < 0)

		return false;



	bit_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;

	if (bit_min < 1)

		return false;



	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &bit_max);

	if (ret < 0)

		return false;



	bit_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;

	if (bit_max < bit_min)

		return false;



	return true;

}



static bool

intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)

{
@@ -625,12 +653,14 @@ intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector) 
		return true;

	}



	if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {

	if (drm_edp_backlight_supported(intel_dp->edp_dpcd) &&

	    check_if_vesa_backlight_possible(intel_dp)) {

		drm_dbg_kms(display->drm,

			    "[CONNECTOR:%d:%s] AUX Backlight Control Supported!\n",

			    connector->base.base.id, connector->base.name);

		return true;

	}



	return false;

}