drm: Add retries for lspcon mode detection

From the CI builds, its been observed that during a driver
reload/insert, dp dual mode read function sometimes fails to
read from LSPCON device 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)
V3: Addressed review comments from Ville/Imre (Add the retries
    exclusively for LSPCON, not for all dp_dual_mode devices)
V4: Added r-b from Imre, sending it to dri-devel (Jani)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102294
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102295
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102359
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103186
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1507826408-19322-1-git-send-email-shashank.sharma@intel.com

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 0ef9011a1856358b2bc6104973888a69f76db8e7..02a50929af6759ab7769bba100134b2e6f4b0713 100644 (file)
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -410,6 +410,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
 {
        u8 data;
        int ret = 0;
+       int retry;
 
        if (!mode) {
                DRM_ERROR("NULL input\n");
@@ -417,10 +418,19 @@ 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 = 0; retry < 6; retry++) {
+               if (retry)
+                       usleep_range(500, 1000);
+
+               ret = drm_dp_dual_mode_read(adapter,
+                                           DP_DUAL_MODE_LSPCON_CURRENT_MODE,
+                                           &data, sizeof(data));
+               if (!ret)
+                       break;
+       }
+
        if (ret < 0) {
-               DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
+               DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
                return -EFAULT;
        }