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

> -----Original Message-----
> From: Mathieu Poirier <[email protected]>
> Sent: Tuesday, July 14, 2026 11:36 AM
> To: Shenwei Wang (OSS) <[email protected]>
> Cc: Linus Walleij <[email protected]>; Bartosz Golaszewski <[email protected]>;
> Jonathan Corbet <[email protected]>; Rob Herring <[email protected]>; Krzysztof
> Kozlowski <[email protected]>; Conor Dooley <[email protected]>; Bjorn
> Andersson <[email protected]>; Frank Li <[email protected]>; Sascha Hauer
> <[email protected]>; Shuah Khan <[email protected]>; linux-
> [email protected]; [email protected]; [email protected];
> Pengutronix Kernel Team <[email protected]>; Fabio Estevam
> <[email protected]>; Shenwei Wang <[email protected]>; Peng Fan
> <[email protected]>; [email protected]; linux-
> [email protected]; [email protected]; linux-arm-
> [email protected]; dl-linux-imx <[email protected]>; Arnaud
> POULIQUEN <[email protected]>; [email protected]; Andrew Lunn
> <[email protected]>
> 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.


> >
> > 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.

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
> > > >