[PATCH v4 2/2] drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

[Kuogee Hsieh]

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 v4:
-- split into two patches

Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
---
 drivers/gpu/drm/msm/dp/dp_link.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
index 36f0af0..7b5ecf5 100644
--- a/drivers/gpu/drm/msm/dp/dp_link.c
+++ b/drivers/gpu/drm/msm/dp/dp_link.c
@@ -49,23 +49,26 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 					struct dp_link_info *link)
 {
 	u8 value;
-	int err;
+	ssize_t len;
+	int i;
 
 	if (link->revision < 0x11)
 		return 0;
 
-	err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
-	if (err < 0)
-		return err;
+	len = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
+	if (len < 0)
+		return len;
 
 	value &= ~DP_SET_POWER_MASK;
 	value |= DP_SET_POWER_D0;
 
-	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
-	if (err < 0)
-		return err;
-
-	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;
 }
-- 
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