Re: [PATCH v14 1/5] docs: driver-api: gpio: rpmsg gpio driver over rpmsg bus

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Tue, Jul 14, 2026 at 07:04:08PM +0000, Shenwei Wang (OSS) wrote:
> 
> 
> > -----Original Message-----
> > From: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Sent: Monday, July 13, 2026 12:17 PM
> > To: Shenwei Wang (OSS) <shenwei.wang@oss.nxp.com>
> > Cc: Linus Walleij <linusw@kernel.org>; Bartosz Golaszewski <brgl@kernel.org>;
> > Jonathan Corbet <corbet@lwn.net>; Rob Herring <robh@kernel.org>; Krzysztof
> > Kozlowski <krzk+dt@kernel.org>; Conor Dooley <conor+dt@kernel.org>; Bjorn
> > Andersson <andersson@kernel.org>; Frank Li <frank.li@nxp.com>; Sascha Hauer
> > <s.hauer@pengutronix.de>; Shuah Khan <skhan@linuxfoundation.org>; linux-
> > gpio@vger.kernel.org; linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
> > Pengutronix Kernel Team <kernel@pengutronix.de>; Fabio Estevam
> > <festevam@gmail.com>; Shenwei Wang <shenwei.wang@nxp.com>; Peng Fan
> > <peng.fan@nxp.com>; devicetree@vger.kernel.org; linux-
> > remoteproc@vger.kernel.org; imx@lists.linux.dev; linux-arm-
> > kernel@lists.infradead.org; dl-linux-imx <linux-imx@nxp.com>; Arnaud
> > POULIQUEN <arnaud.pouliquen@foss.st.com>; b-padhi@ti.com; Andrew Lunn
> > <andrew@lunn.ch>
> > Subject: Re: [PATCH v14 1/5] docs: driver-api: gpio: rpmsg gpio driver over rpmsg
> > bus
> > 
> > > +
> > > +The RPMSG message consists of a 8-byte packet with the following layout:
> > > +
> > > +.. code-block:: none
> > > +.. code-block:: none
> > > +
> > > +   +------+------+--------+
> > > +   | 0x00 | 0x01 |  0x02  |
> > > +   |   2  | line | trigger|
> > > +   +------+------+--------+
> > 
> > 2 things here:
> > 
> > 1) You did not include messages that mask and unmask interrupts at the driver
> > side.
> > 
> > 2) We are carrying virtio-gpio messages on top of RPMSG and as such, this whole
> > protocol should be about thar:
> > 
> > +------+------+--------+--------
> > | 0x00 |       payload         |
> > |  Q   |                       |
> > +------+------+--------+--------
> > 
> > Q = 0 requestq
> > Q = 1 eventq
> > 
> > The "payload" part is simply the format of the messages as found in the virtio-
> > gpio specification.  From there, the only thing left to mention is which messages
> > are not supported, i.e get line names.
> > 
> > > +
> > > +- **line**: The GPIO line (pin) index of the port.
> > > +
> > > +- **trigger**: Optional parameter to indicate the trigger event type.
> > 
> > Not part of the spec - remove.
> > 
> 
> The two fields above are required for rpmsg-gpio, but not for virtio-gpio.

I agree that the line is required but not the trigger.  The driver (using the
same terminology as the specification) knows what trigger the pin has been
configured for.  Adding the trigger information to the interrupt notification is
redundant.

> 
> In the rpmsg-gpio case, interrupt detection and handling occur on the remote processor. The 
> interrupt information (such as the GPIO line and trigger type) must therefore be sent to Linux 
> through this notification message.
> 
> In contrast, for virtio-gpio, interrupt handling is performed on the local processor. Since Linux already 
> has all the necessary interrupt context, the information is not needed.
> 
> Shenwei
> 
> > Given the refactoring work that is still needed, I will not look at the
> > implementation.
> > 
> > Thanks,
> > Mathieu
> > 
> > > +
> > > diff --git a/Documentation/driver-api/gpio/index.rst
> > > b/Documentation/driver-api/gpio/index.rst
> > > index bee58f709b9a..e5eb1f82f01f 100644
> > > --- a/Documentation/driver-api/gpio/index.rst
> > > +++ b/Documentation/driver-api/gpio/index.rst
> > > @@ -16,6 +16,7 @@ Contents:
> > >     drivers-on-gpio
> > >     bt8xxgpio
> > >     pca953x
> > > +   gpio-rpmsg
> > >
> > >  Core
> > >  ====
> > > --
> > > 2.43.0
> > >