[4.2.y-ckt stable] Patch "drm/dp: move hw_mutex up the call stack" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drm/dp: move hw_mutex up the call stack

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 89dcbeb1528cb10d37ebe27db2ab3815a56642a7 Mon Sep 17 00:00:00 2001
From: Rob Clark <robdclark at gmail.com>
Date: Thu, 25 Feb 2016 16:15:05 -0500
Subject: drm/dp: move hw_mutex up the call stack
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 7779c5e23c5132c22a219f1f5554ef81dd15ee91 upstream.

1) don't let other threads trying to bang on aux channel interrupt the
defer timeout/logic
2) don't let other threads interrupt the i2c over aux logic

Technically, according to people who actually have the DP spec, this
should not be required.  In practice, it makes some troublesome Dell
monitor (and perhaps others) work, so probably a case of "It's compliant
if it works with windows" on the hw vendor's part..

v2: rebased to come before DPCD/AUX logging patch for easier backport
to stable branches.

Reported-by: Dave Wysochanski <dwysocha at redhat.com>
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1274157
Signed-off-by: Rob Clark <robdclark at gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Dave Airlie <airlied at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 80a02a4..e62ac37 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -176,7 +176,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 {
 	struct drm_dp_aux_msg msg;
 	unsigned int retry;
-	int err;
+	int err = 0;

 	memset(&msg, 0, sizeof(msg));
 	msg.address = offset;
@@ -184,6 +184,8 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 	msg.buffer = buffer;
 	msg.size = size;

+	mutex_lock(&aux->hw_mutex);
+
 	/*
 	 * The specification doesn't give any recommendation on how often to
 	 * retry native transactions. We used to retry 7 times like for
@@ -192,25 +194,24 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 	 */
 	for (retry = 0; retry < 32; retry++) {

-		mutex_lock(&aux->hw_mutex);
 		err = aux->transfer(aux, &msg);
-		mutex_unlock(&aux->hw_mutex);
 		if (err < 0) {
 			if (err == -EBUSY)
 				continue;

-			return err;
+			goto unlock;
 		}


 		switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
 		case DP_AUX_NATIVE_REPLY_ACK:
 			if (err < size)
-				return -EPROTO;
-			return err;
+				err = -EPROTO;
+			goto unlock;

 		case DP_AUX_NATIVE_REPLY_NACK:
-			return -EIO;
+			err = -EIO;
+			goto unlock;

 		case DP_AUX_NATIVE_REPLY_DEFER:
 			usleep_range(400, 500);
@@ -219,7 +220,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 	}

 	DRM_DEBUG_KMS("too many retries, giving up\n");
-	return -EIO;
+	err = -EIO;
+
+unlock:
+	mutex_unlock(&aux->hw_mutex);
+	return err;
 }

 /**
@@ -441,9 +446,7 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 	 * before giving up the AUX transaction.
 	 */
 	for (retry = 0, defer_i2c = 0; retry < (7 + defer_i2c); retry++) {
-		mutex_lock(&aux->hw_mutex);
 		ret = aux->transfer(aux, msg);
-		mutex_unlock(&aux->hw_mutex);
 		if (ret < 0) {
 			if (ret == -EBUSY)
 				continue;
@@ -570,6 +573,8 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,

 	memset(&msg, 0, sizeof(msg));

+	mutex_lock(&aux->hw_mutex);
+
 	for (i = 0; i < num; i++) {
 		msg.address = msgs[i].addr;
 		msg.request = (msgs[i].flags & I2C_M_RD) ?
@@ -613,6 +618,8 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 	msg.size = 0;
 	(void)drm_dp_i2c_do_msg(aux, &msg);

+	mutex_unlock(&aux->hw_mutex);
+
 	return err;
 }

--
2.7.4