linux-kernel - [PATCH v2 0/4] rpmsg: char: introduce the rpmsg-raw channel

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Message-ID: <20210623150504.14450-1-arnaud.pouliquen@foss.st.com>
Date:   Wed, 23 Jun 2021 17:05:00 +0200
From:   Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <julien.massot@....bzh>, <arnaud.pouliquen@...s.st.com>
Subject: [PATCH v2 0/4] rpmsg: char: introduce the rpmsg-raw channel

Purpose:
  Allow the remote processor to instantiate a /dev/rpmsgX interface relying on the NS announcement
  of the "rpmsg-raw" service.
  This patchet is extracted from  the series [1] with rework to add rpmsg_create_default_ept helper.

Aim:
  There is no generic sysfs interface based on RPMsg that allows a user application to communicate
  with a remote processor in a simple way.
  The rpmsg_char dev solves a part of this problem by allowing an endpoint to be created on the
  local side. But it does not take advantage of the NS announcement mechanism implemented for some
  backends such as the virtio backend. So it is not possible to probe it from  a remote initiative.
  Extending the char rpmsg device to support NS announcement makes the rpmsg_char more generic.
  By announcing a "rpmg-raw" service, the firmware of a remote processor will be able to
  instantiate a /dev/rpmsgX interface providing to the user application a basic link to communicate
  with it without any knowledge of the rpmsg protocol.

Implementation details:
  - Register a rpmsg driver for the rpmsg_char driver, associated to the "rpmsg-raw" channel service.
  - In case of rpmsg char device instantiated by the rpmsg bus (on NS announcement) manage the 
    channel default endpoint to ensure a stable default endpoint address, for communication with 
    the remote processor.

delta vs V1 [2]:
- Rework __rpmsg_chrdev_create_eptdev to return rpmsg_eptdev struct (to use it as private
  data parameter on the rpmsg_create_default_ept call).
- Create default endpoint in the rpmsg_eptdev_open instead of in the open function.
- Squash " rpmsg: char: Return error if user tries to destroy a default endpoint" patch in 
  "rpmsg: char: Add possibility to create and reuse default endpoint" patch.
- Suppress Tested-by: Julien Massot <julien.massot@....bzh>, as updates can impact the test result.

How to test it:
  - This series can be applied on git/andersson/remoteproc.git for-next branch (dc0e14fa833b)
    + the "Restructure the rpmsg char to decorrelate the control part" series[3]

[1] https://patchwork.kernel.org/project/linux-remoteproc/list/?series=475217
[2] https://patchwork.kernel.org/project/linux-remoteproc/list/?series=495557
[3] https://patchwork.kernel.org/project/linux-remoteproc/list/?series=483793

Arnaud Pouliquen (4):
  rpmsg: Introduce rpmsg_create_default_ept function
  rpmsg: char: Introduce __rpmsg_chrdev_create_eptdev function
  rpmsg: char: Add possibility to use default endpoint of the rpmsg
    device.
  rpmsg: char: Introduce the "rpmsg-raw" channel

 drivers/rpmsg/rpmsg_char.c | 120 ++++++++++++++++++++++++++++++++++---
 drivers/rpmsg/rpmsg_core.c |  51 ++++++++++++++++
 include/linux/rpmsg.h      |  13 ++++
 3 files changed, 175 insertions(+), 9 deletions(-)

-- 
2.17.1