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

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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: 40d2f58209 ("drm/i915/backlight: Remove try_vesa_interface")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Pranay Samala <pranay.samala@intel.com>
Link: https://patch.msgid.link/20260316031850.81794-1-suraj.kandpal@intel.com
This commit is contained in:
Suraj Kandpal
2026-03-16 08:48:51 +05:30
parent 3ccc8a9229
commit 0fb03890d1
1 changed files with 31 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
View File

@@ -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;
}