drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

Bring sink out of D3 (power down) mode into D0 (normal operation) mode
by setting DP_SET_POWER_D0 bit to DP_SET_POWER dpcd register. This
patch will retry 3 times if written to DP_SET_POWER register failed.

Changes in v5:
-- split into two patches

Signed-off-by: Kuogee Hsieh <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/502536/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>

Author: Kuogee Hsieh

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

@@ -50,6 +50,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 {
 	u8 value;
 	ssize_t len;
+	int i;
 
 	if (link->revision < 0x11)
 		return 0;
@@ -61,11 +62,13 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 	value &= ~DP_SET_POWER_MASK;
 	value |= DP_SET_POWER_D0;
 
-	len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
-	if (len < 0)
-		return len;
-
-	usleep_range(1000, 2000);
+	/* retry for 1ms to give the sink time to wake up */
+	for (i = 0; i < 3; i++) {
+		len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+		usleep_range(1000, 2000);
+		if (len == 1)
+			break;
+	}
 
 	return 0;
 }