drm/i915/dpcd_bl: Cleanup intel_dp_aux_vesa_enable_backlight() a bit

Get rid of the extraneous switch case in here, and just open code
edp_backlight_mode as we only ever use it once.

v4:
* Check that backlight mode is DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD, not
  DP_EDP_BACKLIGHT_CONTROL_MODE_MASK - imirkin
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514181504.565252-4-lyude@redhat.com

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

@@ -382,7 +382,7 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	struct intel_panel *panel = &connector->panel;
-	u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
+	u8 dpcd_buf, new_dpcd_buf;
 	u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
 
 	if (drm_dp_dpcd_readb(&intel_dp->aux,
@@ -393,12 +393,8 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 	}
 
 	new_dpcd_buf = dpcd_buf;
-	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
 
-	switch (edp_backlight_mode) {
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
+	if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
 		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
 		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
 
@@ -406,13 +402,6 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 				       pwmgen_bit_count) != 1)
 			drm_dbg_kms(&i915->drm,
 				    "Failed to write aux pwmgen bit count\n");
-
-		break;
-
-	/* Do nothing when it is already DPCD mode */
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
-	default:
-		break;
 	}
 
 	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {