linux-kernel - Re: [PATCH v5 3/4] rpmsg: Move the rpmsg control device from rpmsg_char to rpmsg

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Date:   Fri, 15 Oct 2021 23:46:43 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v5 3/4] rpmsg: Move the rpmsg control device from
 rpmsg_char to rpmsg_ctrl

On Mon 11 Oct 05:46 CDT 2021, Arnaud POULIQUEN wrote:

> 
> 
> On 10/9/21 1:35 AM, Bjorn Andersson wrote:
> > On Mon 12 Jul 05:37 PDT 2021, Arnaud Pouliquen wrote:
> > 
> >> Create the rpmsg_ctrl.c module and move the code related to the
> >> rpmsg_ctrldev device in this new module.
> >>
> >> Add the dependency between rpmsg_char and rpmsg_ctrl in the
> >> kconfig file.
> >>
> > 
> > As I said in the cover letter, the only reason I can see for doing this
> > refactoring is in relation to the introduction of
> > RPMSG_CREATE_DEV_IOCTL. So I would like this patch to go together with
> > that patch, together with a good motivation why there's merit to
> > creating yet another kernel module (and by bind/unbind can't be used).
> > 
> > Perhaps I'm just missing some good usecase related to this?
> 
> 
> > 
> >> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
> >> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> >> ---
> >>  drivers/rpmsg/Kconfig      |   9 ++
> >>  drivers/rpmsg/Makefile     |   1 +
> >>  drivers/rpmsg/rpmsg_char.c | 170 +----------------------------
> >>  drivers/rpmsg/rpmsg_char.h |   2 +
> >>  drivers/rpmsg/rpmsg_ctrl.c | 215 +++++++++++++++++++++++++++++++++++++
> >>  5 files changed, 229 insertions(+), 168 deletions(-)
> >>  create mode 100644 drivers/rpmsg/rpmsg_ctrl.c
> >>
> > [..]
> >> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> > [..]
> >> -static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
> >> -{
> > [..]
> >> -	dev = &ctrldev->dev;
> >> -	device_initialize(dev);
> >> -	dev->parent = &rpdev->dev;
> >> -	dev->class = rpmsg_class;
> > [..]
> >> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> > [..]
> >> +static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev)
> >> +{
> > [..]
> >> +	dev = &ctrldev->dev;
> >> +	device_initialize(dev);
> >> +	dev->parent = &rpdev->dev;
> > 
> > You lost the assignment of dev->class here, which breaks the udev rules
> > we use to invoke rpmsgexport to create endpoints and it causes udevadm
> > to complain that rpmsg_ctrlN doesn't have a "subsystem".
> 
> We discussed this point with Mathieu, as a first step i kept the class, but that
> generated another dependency with the rpmsg_char device while information was
> available on the rpmsg bus. The char device and ctrl device should share the
> same class. As rpmsg_ctrl is created first it would have to create the class,and
> provide an API to rpmsg char
> 

Perhaps if this is considered a common piece shared between multiple
rpmsg modules we can create such class in the rpmsg "core" itself?

> Please could you details what does means "rpmsg_ctrlN doesn't have a
> "subsystem"." What exactly the udev is looking for? could it base it check on
> the /dev/rpmsg_ctrl0 or /sys/bus/rpmsg/devices/...?
> 

If I read the uevent messages correctly they seem to contain a SUBSYTEM=
property when the class is provided. But I'm not sure about the reasons
for that.

Regards,
Bjorn

> Thanks,
> Arnaud
> 
> > 
> > Regards,
> > Bjorn
> >