drm/msm/dp: Replace open-coded drm_dp_read_dpcd_caps()

This function duplicates the common function drm_dp_read_dpcd_caps().
The array of DPCD registers filled in is one size larger than the
function takes, but from what I can tell that extra byte was never used.
Resize the array and use the common function to reduce the code here.

Cc: Vinod Polimera <quic_vpolimer@quicinc.com>
Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/554981/
Link: https://lore.kernel.org/r/20230829184735.2841739-2-swboyd@chromium.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_panel.c

@@ -48,47 +48,15 @@ static int dp_panel_read_dpcd(struct dp_panel *dp_panel)
 	ssize_t rlen;
 	struct dp_panel_private *panel;
 	struct dp_link_info *link_info;
-	u8 *dpcd, major = 0, minor = 0, temp;
-	u32 offset = DP_DPCD_REV;
+	u8 *dpcd, major, minor;
 
+	panel = container_of(dp_panel, struct dp_panel_private, dp_panel);
 	dpcd = dp_panel->dpcd;
+	rc = drm_dp_read_dpcd_caps(panel->aux, dpcd);
+	if (rc)
+		return rc;
 
-	panel = container_of(dp_panel, struct dp_panel_private, dp_panel);
 	link_info = &dp_panel->link_info;
-
-	rlen = drm_dp_dpcd_read(panel->aux, offset,
-			dpcd, (DP_RECEIVER_CAP_SIZE + 1));
-	if (rlen < (DP_RECEIVER_CAP_SIZE + 1)) {
-		DRM_ERROR("dpcd read failed, rlen=%zd\n", rlen);
-		if (rlen == -ETIMEDOUT)
-			rc = rlen;
-		else
-			rc = -EINVAL;
-
-		goto end;
-	}
-
-	temp = dpcd[DP_TRAINING_AUX_RD_INTERVAL];
-
-	/* check for EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT */
-	if (temp & BIT(7)) {
-		drm_dbg_dp(panel->drm_dev,
-				"using EXTENDED_RECEIVER_CAPABILITY_FIELD\n");
-		offset = DPRX_EXTENDED_DPCD_FIELD;
-	}
-
-	rlen = drm_dp_dpcd_read(panel->aux, offset,
-		dpcd, (DP_RECEIVER_CAP_SIZE + 1));
-	if (rlen < (DP_RECEIVER_CAP_SIZE + 1)) {
-		DRM_ERROR("dpcd read failed, rlen=%zd\n", rlen);
-		if (rlen == -ETIMEDOUT)
-			rc = rlen;
-		else
-			rc = -EINVAL;
-
-		goto end;
-	}
-
 	link_info->revision = dpcd[DP_DPCD_REV];
 	major = (link_info->revision >> 4) & 0x0f;
 	minor = link_info->revision & 0x0f;

drivers/gpu/drm/msm/dp/dp_panel.h

@@ -13,8 +13,6 @@
 
 struct edid;
 
-#define DPRX_EXTENDED_DPCD_FIELD	0x2200
-
 #define DP_DOWNSTREAM_PORTS		4
 #define DP_DOWNSTREAM_CAP_SIZE		4
 
@@ -40,7 +38,7 @@ struct dp_panel_psr {
 
 struct dp_panel {
 	/* dpcd raw data */
-	u8 dpcd[DP_RECEIVER_CAP_SIZE + 1];
+	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 	u8 ds_cap_info[DP_DOWNSTREAM_PORTS * DP_DOWNSTREAM_CAP_SIZE];
 	u32 ds_port_cnt;
 	u32 dfp_present;