[PATCH] drm/i915/backlight: Fix VESA backlight possible check condition

[Suraj Kandpal <suraj.kandpal@intel.com>]

VESA backlight is possible through AUX only when
BACKLIGHT_AUX_ENABLE_CAPABLE is true or when we use BL_ENABLE bit
to enable backlight. Since that is not implemented we need to make
sure we do not try to manipulate backlight when
BACKLIGHT_AUX_ENABLE_CAPABLE is not set.
Also fix return value when condition is not fulfilled.

Fixes: 40d2f5820951 ("drm/i915/backlight: Remove try_vesa_interface")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

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 d0c76632a946..138d5b5e5482 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -615,8 +615,9 @@ 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;
+	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP &&
+	      intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
+		return false;
 
 	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
 	if (ret < 0)
-- 
2.34.1