On Thu 22 Apr 21:12 CDT 2021, Siddharth Gupta wrote:Okay, I will make the appropriate changes. Thanks!
On 4/22/2021 11:04 AM, Mathieu Poirier wrote:Your patch is correct, we need to cdev_add() and in particular assign
Hi Siddharth,Okay sure, I will remove it.
On Tue, Apr 20, 2021 at 12:26:45PM -0700, Siddharth Gupta wrote:
When cdev_add is called after device_add has been called there is noPlease don't add this kind of reference to the change log as it will become
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
invalid with time.
Not sure what you mean here Mathieu? The reason why we can't useway to use these APIs is to call cdev_add before device_add is called.Please explain why the existing API can't be used directly.
Since the cdev is an optional feature for remoteproc we cannot directly
use the existing API.
it is because cdev is an optional feature. We would either have to move
device_add inside rproc_char_dev_add or the other way around and
make cdev a regular feature. Since device_add can't be called on the
same device struct twice[1], we have to do things this way. Also this
way we don't have to rely on the userspace to call mknod as it will
be called[2] as a part of the device_add call in devtmpfs_create_node.
Now that I think about it, is the above what you want me to put in the
commit text? :)
dev->devt before calling device_add(). Given how the code is split in
core and cdev there's no way to use cdev_device_add(), but I don't think
anyone is suggesting that - except for your commit message.
So while everything you mention in your commit message seems correct,
you should be able to make it more to the point by distilling it down to
something like:
The cdev needs to be added and devt assigned before device_add() is
called in order for the relevant sysfs and devtmpfs entries to be
created and the uevent to be properly populated.
Yes exactly! We were just lucky till now :)[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/base/core.c#n3105So it works for e.g. systemd based systems (most of the time), while in
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/base/devtmpfs.c#n215
It is a sporadic issue due to a race between the userspace uevent handlerHence moving rproc_char_device_add() beforeI have tested this change and it works. So how did it work 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@xxxxxxxxxxxxxx>
---
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;
+
and cdev_add. If the uevent for the device is received/processed after
cdev_add the cdev is created.
If "add" is written to the uevent file or mknod is manually called for devt
the cdev works as expected, just that the sysfs links won't be created.
a system based on devtmpfs the dev node would never show up.
Regards,
Bjorn
Sure. I'll make those changes.ret = device_add(dev);While reviewing this patch I had another look at rproc_add() and noticed it
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;
-
doesn't clean up after itself in case of failure. If any of the conditions
aren't met the function returns but rproc_delete_debug_dir(),
rproc_char_device_remove() and device_del() aren't called. Please fix that as
part of your next revision.
Thanks,
Sid
Thanks,
Mathieu
/* if rproc is marked always-on, request it to boot */
if (rproc->auto_boot) {
ret = rproc_trigger_auto_boot(rproc);
--
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