Hi Suraj,
> -----Original Message----- > From: Intel-xe <[email protected]> On Behalf Of Suraj > Kandpal > Sent: Monday, March 9, 2026 11:10 AM > To: [email protected]; [email protected] > Cc: Kandpal, Suraj <[email protected]> > Subject: [PATCH] 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 As per the spec, bit_min should be >=1 which code correctly checks. Please update the commit message to min >=1. > 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; This aux_set variable seems unnecessary. The check can be simplified without this temporary variable as below, if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) return true; Regards, Pranay > + > + 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
