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

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Message-ID: <ffb110dc-bc3b-dbc2-679f-de2416f7b90f@foss.st.com>
Date:   Mon, 18 Oct 2021 11:13:04 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
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 10/16/21 6:46 AM, Bjorn Andersson wrote:
> 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?

Yes that seems a good alternative

> 
>> 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.

If it part of the udev requirement, i suppose that it is mandatory, and in this
case, declare the class in the core make sense.

I will send a new patchset that will squash all the remaining patches, taking
into account your comment.

Thanks,
Arnaud

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