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 06:43:30PM +0000, Shenwei Wang (OSS) wrote:
> 
> 
> > -----Original Message-----
> > From: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Sent: Tuesday, July 14, 2026 11:36 AM
> > 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
> > 
> > On Tue, Jul 14, 2026 at 02:29:12PM +0000, Shenwei Wang (OSS) wrote:
> d
> > > > > +  - 3: Both edge trigger
> > > > > +  - 4: High level trigger
> > > > > +  - 8: Low level trigger
> > > >
> > > > I'm in agreement with cmd 3, 4, 5 and 6.
> > > >
> > >
> > > How about cmd 2?
> > 
> > Yes, I forgot cmd 2.
> > 
> > >
> > > > > +
> > > > > +**Reply:**
> > > > > +
> > > > > +.. code-block:: none
> > > > > +
> > > > > +   +------+--------+--------+
> > > > > +   | 0x00 |  0x01  |  0x02  |
> > > > > +   |   1  | status |    0   |
> > > > > +   +------+--------+--------+
> > > > > +
> > > > > +- **status**:
> > > > > +
> > > > > +  - 0: Ok
> > > > > +  - 1: Error
> > > > > +
> > > > > +SET_WAKEUP (Cmd=16)
> > > > > +~~~~~~~~~~~~~~~~~~~
> > > >
> > > > I already commented on messages that are not part of the virtio-gpio
> > > > specification.
> > > >
> > >
> > > I don't believe virtio-gpio needs a SET_WAKEUP command.
> > >
> > > In the RPMSG case, SET_WAKEUP is required because it performs an
> > > operation on the remote processor, so the remote side must be explicitly
> > notified.
> > 
> > What operations would that be?
> > 
> 
> The operation is enabling the line as a wakeup source. In practice, this involves configuring 
> hardware-specific wakeup settings (e.g., register bits) on the remote processor, so the remote 
> side must be explicitly notified through SET_WAKEUP.
>

As I said before, we are not enhancing the virtio-gpio specification.  If the
functionality is not part of the specification, it is not part of this protocol.
 
> 
> > >
> > > For virtio-gpio, however, everything is handled locally. The other
> > > side does not need to perform any action, so sending a SET_WAKEUP command
> > appears unnecessary.
> > 
> > What is "everything"?
> > 
> 
> I mean masking, unmasking, and marking the interrupt as a wakeup source. All of 
> these operations are handled on local processor.

There may be enough capability in your remote processor to do all that, but we
can't assume the same applies to all implementations.  rpmsg-gpio is not about
inventing a new protocol or delegating actions to the remote processor.  It is
about carrying virtio-gpio packets on top of RPMSG.  It needs to operate
_exactly_ the same way as virtio-gpio.

> 
> Shenwei
> 
> > >
> > >
> > > > > +
> > > > > +**Request:**
> > > > > +
> > > > > +.. code-block:: none
> > > > > +
> > > > > +   +------+------+------+------+------+------+------+------+
> > > > > +   | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 |
> > > > > +   |      1      |    line     |           value           |
> > > > > +   +------+------+------+------+------+------+------+------+
> > > > > +
> > > > > +- **value**: Wakeup enable.
> > > > > +
> > > > > +  The remote system should always aim to stay in a
> > > > > + power-efficient state by  shutting down or clock-gating the GPIO
> > > > > + blocks that aren't in use. Since  the remoteproc driver is
> > > > > + responsible for managing the power states of the  remote
> > > > > + firmware, the GPIO driver does not require to know the firmware's
> > running states.
> > > > > +
> > > > > +  When the wakeup bit is set, the remote firmware should
> > > > > + configure the line  as a wakeup source. The firmware should send
> > > > > + the notification message to  Linux after it is woken from the GPIO line.
> > > > > +
> > > > > +  - 0: Disable wakeup from GPIO
> > > > > +  - 1: Enable wakeup from GPIO
> > > > > +
> > > > > +**Reply:**
> > > > > +
> > > > > +.. code-block:: none
> > > > > +
> > > > > +   +------+--------+--------+
> > > > > +   | 0x00 |  0x01  |  0x02  |
> > > > > +   |   1  | status |    0   |
> > > > > +   +------+--------+--------+
> > > > > +
> > > > > +- **status**:
> > > > > +
> > > > > +  - 0: Ok
> > > > > +  - 1: Error
> > > > > +
> > > > > +Notification Message
> > > > > +--------------------
> > > >
> > > > "Interrupt Messages"
> > > >
> > > > > +
> > > > > +Notifications are sent by the remote core and they have
> > > > > +**Type=2 (GPIO_RPMSG_NOTIFY)**:
> > > > > +
> > > > > +When a GPIO line asserts an interrupt on the remote processor,
> > > > > +the firmware should immediately mask the corresponding interrupt
> > > > > +source and send a notification message to the Linux. Upon
> > > > > +completion of the interrupt handling on the Linux side, the
> > > > > +driver should issue a command **SET_IRQ_TYPE** to the firmware to
> > unmask the interrupt.
> > > > > +
> > > > > +A Notification message can arrive between a SEND and its REPLY
> > > > > +message, and the driver is expected to handle this scenario.
> > > > > +
> > > > > +.. 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.
> > >
> > > Interrupt masking and unmasking are handled entirely on the local processor.
> > >
> > > When an interrupt occurs, the remote system masks the interrupt and
> > > then sends a notification to Linux. After Linux processes the
> > > notification, it sends a SET_IRQ_TYPE message back to the remote system,
> > which then unmasks the interrupt.
> > 
> > This is the kind of information that should be part of this documentation.
> > 
> > >
> > > Thanks,
> > > Shenwei
> > >
> > > >
> > > > 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.
> > > >
> > > > 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
> > > > >