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SubjectRe: [PATCH] remoteproc: core: Move cdev add before device add
Hi Siddharth,

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 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

Please don't add this kind of reference to the change log as it will become
invalid with time.

> 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.

Please explain why the existing API can't be used directly.

> 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@codeaurora.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;
> +

I have tested this change and it works. So how did it work before?

> 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;
> -

While reviewing this patch I had another look at rproc_add() and noticed it
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,
Mathieu


> /* if rproc is marked always-on, request it to boot */
> if (rproc->auto_boot) {
> ret = rproc_trigger_auto_boot(rproc);
> --
> Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>

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