Patch "drm: Add retries for lspcon mode detection" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

drm: Add retries for lspcon mode detection

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-add-retries-for-lspcon-mode-detection.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Shashank Sharma <[email protected]>
Date: Thu, 12 Oct 2017 22:10:08 +0530
Subject: drm: Add retries for lspcon mode detection

From: Shashank Sharma <[email protected]>

[ Upstream commit f687e25a7a245952349f1f9f9cc238ac5a3be258 ]

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

---
 drivers/gpu/drm/drm_dp_dual_mode_helper.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

@@ -410,6 +410,7 @@ int drm_lspcon_get_mode(struct i2c_adapt
 {
 	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_adapt
 	}
 
 	/* 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;
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/drm-add-retries-for-lspcon-mode-detection.patch