Re: [PATCH v8 11/13] rpmsg: char: Introduce the "rpmsg-raw" channel

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Tue 18 Jan 05:04 CST 2022, Arnaud POULIQUEN wrote:

> 
> 
> On 1/18/22 12:03 AM, Bjorn Andersson wrote:
> > On Tue 07 Dec 02:08 CST 2021, Arnaud Pouliquen wrote:
> > 
> > > Allows to probe the endpoint device on a remote name service announcement,
> > > by registering a rpmsg_driverfor the "rpmsg-raw" channel.

Thought of this after replying yesterday, I really would like this to be
updated to include an explanation of _why_ this is a good thing. What is
the use case etc.

> > > 
> > > With this patch the /dev/rpmsgX interface can be instantiated by the remote
> > > firmware.

It would be nice if this mentioned why you can rely on udev events and
rpmsgexport.

> > > 
> > > Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> > > ---
> > >   drivers/rpmsg/rpmsg_char.c | 64 ++++++++++++++++++++++++++++++++++++++
> > >   drivers/rpmsg/rpmsg_ctrl.c |  7 +++--
> > >   2 files changed, 69 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> > > index cf97839f5833..92b44630e03a 100644
> > > --- a/drivers/rpmsg/rpmsg_char.c
> > > +++ b/drivers/rpmsg/rpmsg_char.c
> > > @@ -435,6 +435,58 @@ int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent
> > >   }
> > >   EXPORT_SYMBOL(rpmsg_chrdev_eptdev_create);
> > > +static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
> > > +{
> > > +	struct rpmsg_channel_info chinfo;
> > > +	struct rpmsg_eptdev *eptdev;
> > > +	struct device *dev = &rpdev->dev;
> > > +
> > > +	memcpy(chinfo.name, rpdev->id.name, RPMSG_NAME_SIZE);
> > > +	chinfo.src = rpdev->src;
> > > +	chinfo.dst = rpdev->dst;
> > > +
> > > +	eptdev = rpmsg_chrdev_eptdev_alloc(rpdev, dev);
> > > +	if (IS_ERR(eptdev))
> > > +		return PTR_ERR(eptdev);
> > > +
> > > +	/*
> > > +	 * Create the default endpoint associated to the rpmsg device and provide rpmsg_eptdev
> > > +	 * structure as callback private data.
> > 
> > If the only this the probe function does is to create a new endpoint
> > with the same properties as the rpdev, why can't you just specify a
> > callback on the rpmsg_chrdev_driver?
> > 
> > As this isn't the typical way you create a default endpoint I think the
> > reasoning behind this warrants a proper explanation in the commit
> > message.
> > 
> 
> As mentioned in [PATCH v8 09/13] rpmsg: Introduce rpmsg_create_default_ept function
> "This helper function allows rpmsg drivers to create a default endpoint
> on runtime with an associated private context."
> 
> Here the private context is the eptdev structure. I need to create the
> structure first, before
> the endpoint.
> I will add more details in the commit message as you suggest.

Okay, I think the important part to document is _why_ this has to happen
in this order - in particular since I suspect that this reason might not
be unique to this driver.

> 
> An alternative could be to directly set default_ept->priv but as the
> rpmsg_create_default_ept
> "priv" parameter is forwarded to the rpmsg backend (using create_ept ops).
> This could introduces unexpected side effect.
> 

I'm not sure I understand the unexpected side effect of reassigning priv
here.

Regards,
Bjorn

> > > +	 * Do not allow the creation and release of an endpoint on /dev/rpmsgX open and close,
> > > +	 * reuse the default endpoint instead
> > 
> > This sentence doesn't tell me anything about this code snippet and
> > doesn't indicate that it relates to the snippet added elsewhere in this
> > file by the previous patch.
> > 
> > > +	 */
> > > +	eptdev->default_ept = rpmsg_create_default_ept(rpdev, rpmsg_ept_cb, eptdev, chinfo);
> > > +	if (!eptdev->default_ept) {
> > > +		dev_err(&rpdev->dev, "failed to create %s\n", chinfo.name);
> > > +		put_device(dev);
> > > +		kfree(eptdev);
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	return rpmsg_chrdev_eptdev_add(eptdev, chinfo);
> > > +}
> > > +
> > > +static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
> > > +{
> > > +	int ret;
> > > +
> > > +	ret = device_for_each_child(&rpdev->dev, NULL, rpmsg_chrdev_eptdev_destroy);
> > > +	if (ret)
> > > +		dev_warn(&rpdev->dev, "failed to destroy endpoints: %d\n", ret);
> > > +}
> > > +
> > > +static struct rpmsg_device_id rpmsg_chrdev_id_table[] = {
> > > +	{ .name	= "rpmsg-raw" },
> > > +	{ },
> > > +};
> > > +
> > > +static struct rpmsg_driver rpmsg_chrdev_driver = {
> > > +	.probe = rpmsg_chrdev_probe,
> > > +	.remove = rpmsg_chrdev_remove,
> > > +	.id_table = rpmsg_chrdev_id_table,
> > > +	.drv.name = "rpmsg_chrdev",
> > > +};
> > > +
> > >   static int rpmsg_chrdev_init(void)
> > >   {
> > >   	int ret;
> > > @@ -445,12 +497,24 @@ static int rpmsg_chrdev_init(void)
> > >   		return ret;
> > >   	}
> > > +	ret = register_rpmsg_driver(&rpmsg_chrdev_driver);
> > > +	if (ret < 0) {
> > > +		pr_err("rpmsg: failed to register rpmsg raw driver\n");
> > > +		goto free_region;
> > > +	}
> > > +
> > >   	return 0;
> > > +
> > > +free_region:
> > > +	unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
> > > +
> > > +	return ret;
> > >   }
> > >   postcore_initcall(rpmsg_chrdev_init);
> > >   static void rpmsg_chrdev_exit(void)
> > >   {
> > > +	unregister_rpmsg_driver(&rpmsg_chrdev_driver);
> > >   	unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
> > >   }
> > >   module_exit(rpmsg_chrdev_exit);
> > > diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> > > index 59d2bd264fdb..298e75dc7774 100644
> > > --- a/drivers/rpmsg/rpmsg_ctrl.c
> > > +++ b/drivers/rpmsg/rpmsg_ctrl.c
> > > @@ -10,6 +10,9 @@
> > >    * Based on rpmsg performance statistics driver by Michal Simek, which in turn
> > >    * was based on TI & Google OMX rpmsg driver.
> > >    */
> > > +
> > > +#define pr_fmt(fmt)		KBUILD_MODNAME ": " fmt
> > 
> > These changes seems unrelated to above.
> 
> I apparently broke something in my patchset here during a rebase. The previous
> irrelevant comment you pointed out to me is also a consequence. My apologies
> for this dirty patch...
> 
> Thanks,
> Arnaud
> 
> > 
> > Regards,
> > Bjorn
> > 
> > > +
> > >   #include <linux/cdev.h>
> > >   #include <linux/device.h>
> > >   #include <linux/fs.h>
> > > @@ -193,13 +196,13 @@ static int rpmsg_ctrldev_init(void)
> > >   	ret = alloc_chrdev_region(&rpmsg_major, 0, RPMSG_DEV_MAX, "rpmsg_ctrl");
> > >   	if (ret < 0) {
> > > -		pr_err("rpmsg: failed to allocate char dev region\n");
> > > +		pr_err("failed to allocate char dev region\n");
> > >   		return ret;
> > >   	}
> > >   	ret = register_rpmsg_driver(&rpmsg_ctrldev_driver);
> > >   	if (ret < 0) {
> > > -		pr_err("rpmsg ctrl: failed to register rpmsg driver\n");
> > > +		pr_err("failed to register rpmsg driver\n");
> > >   		unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
> > >   	}
> > > -- 
> > > 2.17.1
> > >