[Intel-gfx] [REBASE v3 1/2] 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 and respond.
- changes one error log's level from ERROR->DEBUG as we want
  to call it an error only after all the retries are exhausted.

V2: Addressed review comments from Jani (for loop for retry)
V3: Addressed review comments from Imre (break on partial read too)

Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
---
 drivers/gpu/drm/drm_dp_dual_mode_helper.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 0ef9011..725b298 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -75,8 +75,16 @@ ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
 		},
 	};
 	int ret;
+	int retry;
+
+	for (retry = 0; retry < 6; retry++) {
+		if (retry)
+			usleep_range(500, 1000);
+		ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
+		if (ret >= 0)
+			break;
+	}
 
-	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
 	if (ret < 0)
 		return ret;
 	if (ret != ARRAY_SIZE(msgs))
@@ -420,7 +428,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
 	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_CURRENT_MODE,
 				    &data, sizeof(data));
 	if (ret < 0) {
-		DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
+		DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
 		return -EFAULT;
 	}
 
-- 
2.7.4