[Intel-gfx] [PATCH 3/3] drm: Add retries for dp dual mode read

[Shashank Sharma]

>From the CI builds, its been observed that during a driver
reload/insert, dp dual mode read function sometimes fails to
read from dual mode devices (like LSPCON) over i2c-over-aux
channel. This patch adds some delay and few retries, allowing
a scope for these devices to settle down.

V3: Introduced this patch

Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
---
 drivers/gpu/drm/drm_dp_dual_mode_helper.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index fc8c7ac..bb34ff8 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -75,8 +75,15 @@ ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
 		},
 	};
 	int ret;
+	int retry;
+
+	for (retry = 5; ; retry--) {
+		ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
+		if (ret > 0 || !retry)
+			break;
+		usleep_range(500, 1000);
+	}
 
-	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
 	if (ret < 0)
 		return ret;
 	if (ret != ARRAY_SIZE(msgs))
-- 
2.7.4