linux-kernel - [PATCH] remoteproc: core: Invoke subdev callbacks in list order

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Date:   Mon, 17 May 2021 16:08:13 -0700
From:   Siddharth Gupta <sidgup@...eaurora.org>
To:     bjorn.andersson@...aro.org, ohad@...ery.com,
        linux-remoteproc@...r.kernel.org
Cc:     Siddharth Gupta <sidgup@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, psodagud@...eaurora.org
Subject: [PATCH] remoteproc: core: Invoke subdev callbacks in list order

Subdevices at the beginning of the subdev list should have
higher priority than those at the end of the list. Reverse
traversal of the list causes priority inversion, which can
impact the performance of the device.

For example a device adds the glink, sysmon and ssr subdevs
to its list. During a crash the ssr notification would go
before the glink and sysmon notifications. This can cause a
degraded response when a client driver waits for a response
from the crashed rproc.

Signed-off-by: Siddharth Gupta <sidgup@...eaurora.org>
---
 drivers/remoteproc/remoteproc_core.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
index 626a6b90f..ac8fc42 100644
--- a/drivers/remoteproc/remoteproc_core.c
+++ b/drivers/remoteproc/remoteproc_core.c
@@ -1167,7 +1167,7 @@ static int rproc_handle_resources(struct rproc *rproc,
 
 static int rproc_prepare_subdevices(struct rproc *rproc)
 {
-	struct rproc_subdev *subdev;
+	struct rproc_subdev *subdev, *itr;
 	int ret;
 
 	list_for_each_entry(subdev, &rproc->subdevs, node) {
@@ -1181,9 +1181,11 @@ static int rproc_prepare_subdevices(struct rproc *rproc)
 	return 0;
 
 unroll_preparation:
-	list_for_each_entry_continue_reverse(subdev, &rproc->subdevs, node) {
-		if (subdev->unprepare)
-			subdev->unprepare(subdev);
+	list_for_each_entry(itr, &rproc->subdevs, node) {
+		if (itr == subdev)
+			break;
+		if (itr->unprepare)
+			itr->unprepare(subdev);
 	}
 
 	return ret;
@@ -1191,7 +1193,7 @@ static int rproc_prepare_subdevices(struct rproc *rproc)
 
 static int rproc_start_subdevices(struct rproc *rproc)
 {
-	struct rproc_subdev *subdev;
+	struct rproc_subdev *subdev, *itr;
 	int ret;
 
 	list_for_each_entry(subdev, &rproc->subdevs, node) {
@@ -1205,9 +1207,11 @@ static int rproc_start_subdevices(struct rproc *rproc)
 	return 0;
 
 unroll_registration:
-	list_for_each_entry_continue_reverse(subdev, &rproc->subdevs, node) {
-		if (subdev->stop)
-			subdev->stop(subdev, true);
+	list_for_each_entry(itr, &rproc->subdevs, node) {
+		if (itr == subdev)
+			break;
+		if (itr->stop)
+			itr->stop(itr, true);
 	}
 
 	return ret;
@@ -1217,7 +1221,7 @@ static void rproc_stop_subdevices(struct rproc *rproc, bool crashed)
 {
 	struct rproc_subdev *subdev;
 
-	list_for_each_entry_reverse(subdev, &rproc->subdevs, node) {
+	list_for_each_entry(subdev, &rproc->subdevs, node) {
 		if (subdev->stop)
 			subdev->stop(subdev, crashed);
 	}
@@ -1227,7 +1231,7 @@ static void rproc_unprepare_subdevices(struct rproc *rproc)
 {
 	struct rproc_subdev *subdev;
 
-	list_for_each_entry_reverse(subdev, &rproc->subdevs, node) {
+	list_for_each_entry(subdev, &rproc->subdevs, node) {
 		if (subdev->unprepare)
 			subdev->unprepare(subdev);
 	}
-- 
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