linux-kernel - [PATCH] remoteproc: core: Move cdev add before device add

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Message-Id: <1618946805-26970-1-git-send-email-sidgup@codeaurora.org>
Date:   Tue, 20 Apr 2021 12:26:45 -0700
From:   Siddharth Gupta <sidgup@...eaurora.org>
To:     bjorn.andersson@...aro.org, ohad@...ery.com,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Siddharth Gupta <sidgup@...eaurora.org>, psodagud@...eaurora.org,
        eberman@...eaurora.org
Subject: [PATCH] remoteproc: core: Move cdev add before device add

When cdev_add is called after device_add has been called there is no
way for the userspace to know about the addition of a cdev as cdev_add
itself doesn't trigger a uevent notification, or for the kernel to
know about the change to devt. This results in two problems:
 - mknod is never called for the cdev and hence no cdev appears on
   devtmpfs.
 - sysfs links to the new cdev are not established.

Based on how cdev_device_add[1] is written, it appears that the correct
way to use these APIs is to call cdev_add before device_add is called.
Since the cdev is an optional feature for remoteproc we cannot directly
use the existing API. Hence moving rproc_char_device_add() before
device_add() in rproc_add().

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/char_dev.c#n537

Signed-off-by: Siddharth Gupta <sidgup@...eaurora.org>
---
 drivers/remoteproc/remoteproc_core.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
index 626a6b90f..562355a 100644
--- a/drivers/remoteproc/remoteproc_core.c
+++ b/drivers/remoteproc/remoteproc_core.c
@@ -2316,6 +2316,11 @@ int rproc_add(struct rproc *rproc)
 	struct device *dev = &rproc->dev;
 	int ret;
 
+	/* add char device for this remoteproc */
+	ret = rproc_char_device_add(rproc);
+	if (ret < 0)
+		return ret;
+
 	ret = device_add(dev);
 	if (ret < 0)
 		return ret;
@@ -2329,11 +2334,6 @@ int rproc_add(struct rproc *rproc)
 	/* create debugfs entries */
 	rproc_create_debug_dir(rproc);
 
-	/* add char device for this remoteproc */
-	ret = rproc_char_device_add(rproc);
-	if (ret < 0)
-		return ret;
-
 	/* if rproc is marked always-on, request it to boot */
 	if (rproc->auto_boot) {
 		ret = rproc_trigger_auto_boot(rproc);
-- 
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