[Intel-gfx] [PATCH v2 1/2] drm: Add retries for lspcon status check

[Shashank Sharma]

It's an observation during some CI tests that few LSPCON chips
respond slow while system is under load, and need some delay
while reading current mode status using i2c-over-aux channel.

This patch:
- Adds few retries and delays before declaring a read
  failure from LSPCON hardware.
- Changes the debug level of the print from ERROR->DEBUG
  whereas another patch in I915 will add an ERROR message
  from the caller when we have timed out all our limits.

V2: addressed review comments from Imre, and added r-b
    - use int instead of u8 for counter
    - use for loop instead of do...while();

Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>

Reviewed-by: Imre Deak <imre.deak at intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar at intel.com>
---
 drivers/gpu/drm/drm_dp_dual_mode_helper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 80e62f6..fc8c7ac 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -409,6 +409,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
 			enum drm_lspcon_mode *mode)
 {
 	u8 data;
+	int retry;
 	int ret = 0;
 
 	if (!mode) {
@@ -417,10 +418,17 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
 	}
 
 	/* Read Status: i2c over aux */
-	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_CURRENT_MODE,
-				    &data, sizeof(data));
+	for (retry = 5; ; retry--) {
+		ret = drm_dp_dual_mode_read(adapter,
+					    DP_DUAL_MODE_LSPCON_CURRENT_MODE,
+					    &data, sizeof(data));
+		if (!ret || !retry)
+			break;
+		usleep_range(500, 1000);
+	}
+
 	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