linux-kernel - Re: [PATCH v5 0/4] Restructure the rpmsg char to decorrelate the control part.

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Date:   Fri, 8 Oct 2021 16:21:02 -0700
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 0/4] Restructure the rpmsg char to decorrelate the
 control part.

On Mon 12 Jul 05:37 PDT 2021, Arnaud Pouliquen wrote:

> Main update from V4 [1] 
>  - complete commit messages with Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>  - rebased on kernel V.14-rc1.
> 
> This series can be applied and tested on "Linux 5.14-rc1"(e73f0f0ee754) branch
> 
> Series description:
> This series is the second step in the division of the series [2]: 
> "Introducing a Generic IOCTL Interface for RPMsg Channel Management".
> 
> The purpose of this patchset is to split the code related to the control
> and the endpoint. The code related to the control part is moved in the rpmsg_ctrl.c.

I'm not convinced about the merits for this refactoring, you're creating
yet another kernel module which is fairly tightly coupled with
the rpmsg_char kernel module and the only case I can see where this
would be useful is if you want to be able to create reach
RPMSG_CREATE_DEV_IOCTL and RPMSG_DESTROY_EPT_IOCTL without having to
include the rpmsg_char part in your kernel.

> This split is an intermediate step to extend the controls to allow user applications to
> instantiate rpmsg devices.
>     

Can you give a concrete example of when this would be used?

Per our previous discussions I believe you intend to use this to bind
your rpmsg_tty driver to arbitrary channels in runtime, which to me
sounds like you're reinventing the bind/unbind sysfs attrs.

Regards,
Bjorn

> Notice that this patchset does not modify the behavior for using the RPMSG_CREATE_EPT_IOCTL
> and RPMSG_DESTROY_EPT_IOCTL controls.
>   
> The next step should be to add the capability to:
> - instantiate rpmsg_chrdev from the remote side (NS announcement),
> - instantiate rpmsg_chrdev from local user application by introducing the
>   IOCTLs RPMSG_CREATE_DEV_IOCTL and RPMSG_DESTROY_DEV_IOCTL to instantiate the rpmsg devices,
> - send a NS announcement to the remote side on rpmsg_chrdev local instantiation.
> 
> [1]: https://patchwork.kernel.org/project/linux-remoteproc/list/?series=483793
> [2]: https://patchwork.kernel.org/project/linux-remoteproc/list/?series=435523
> 
> Arnaud Pouliquen (4):
>   rpmsg: char: Remove useless include
>   rpmsg: char: Export eptdev create an destroy functions
>   rpmsg: Move the rpmsg control device from rpmsg_char to rpmsg_ctrl
>   rpmsg: Update rpmsg_chrdev_register_device function
> 
>  drivers/rpmsg/Kconfig             |   9 ++
>  drivers/rpmsg/Makefile            |   1 +
>  drivers/rpmsg/qcom_glink_native.c |   2 +-
>  drivers/rpmsg/qcom_smd.c          |   2 +-
>  drivers/rpmsg/rpmsg_char.c        | 184 ++-----------------------
>  drivers/rpmsg/rpmsg_char.h        |  51 +++++++
>  drivers/rpmsg/rpmsg_ctrl.c        | 215 ++++++++++++++++++++++++++++++
>  drivers/rpmsg/rpmsg_internal.h    |   8 +-
>  drivers/rpmsg/virtio_rpmsg_bus.c  |   2 +-
>  9 files changed, 293 insertions(+), 181 deletions(-)
>  create mode 100644 drivers/rpmsg/rpmsg_char.h
>  create mode 100644 drivers/rpmsg/rpmsg_ctrl.c
> 
> -- 
> 2.17.1
>