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: 40d2f5820951 ("drm/i915/backlight: Remove try_vesa_interface") Signed-off-by: Suraj Kandpal <[email protected]> --- .../drm/i915/display/intel_dp_aux_backlight.c | 36 ++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c index a7b186d0e3c4..5b6f5c5f00e6 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c @@ -609,6 +609,38 @@ 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; + bool aux_set = false; + u8 bit_min, bit_max; + + if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) + aux_set = true; + + if (!aux_set) + 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 +657,14 @@ 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; } -- 2.34.1
