On Tue, Jul 14, 2026 at 02:29:12PM +0000, Shenwei Wang (OSS) wrote: > > > > -----Original Message----- > > From: Mathieu Poirier <[email protected]> > > Sent: Monday, July 13, 2026 12:17 PM > > 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 Thu, Jun 25, 2026 at 10:54:26AM -0500, Shenwei Wang wrote: > > > From: Shenwei Wang <[email protected]> > > > > > > Describes the gpio rpmsg transport protocol over the rpmsg bus between > > > the remote system and Linux. > > > > > > Signed-off-by: Shenwei Wang <[email protected]> > > > --- > > > Documentation/driver-api/gpio/gpio-rpmsg.rst | 271 +++++++++++++++++++ > > > Documentation/driver-api/gpio/index.rst | 1 + > > > 2 files changed, 272 insertions(+) > > > create mode 100644 Documentation/driver-api/gpio/gpio-rpmsg.rst > > > > > > diff --git a/Documentation/driver-api/gpio/gpio-rpmsg.rst > > > b/Documentation/driver-api/gpio/gpio-rpmsg.rst > > > new file mode 100644 > > > index 000000000000..7d351ff0adb0 > > > --- /dev/null > > > +++ b/Documentation/driver-api/gpio/gpio-rpmsg.rst > > > @@ -0,0 +1,271 @@ > > > +.. SPDX-License-Identifier: GPL-2.0-or-later > > > + > > > +GPIO RPMSG (Remote Processor Messaging) Protocol > > > +================================================ > > > + > > > +The GPIO RPMSG transport protocol is used for communication and > > > +interaction with GPIO controllers on remote processors via the RPMSG bus. > > > + > > > +Message Format > > > +-------------- > > > + > > > +The RPMSG message consists of a 8-byte packet with the following layout: > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | cmd | line | value | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +- **cmd**: Command code, used for GPIO_RPMSG_SEND messages. > > > + > > > +- **line**: The GPIO line (pin) index of the port. > > > > Here and throughout, please remove any mention of 'port'. This is handled > > by the > > endpoint device, i.e one GPIO controller (port) per endpoint. > > > > > + > > > +- **value**: See details in the command description below. > > > + > > > + > > > +GPIO Commands > > > +------------- > > > + > > > +Commands are specified in the **Cmd** field. > > > + > > > +The SEND message is always sent from Linux to the remote firmware. > > > +Each SEND corresponds to a single REPLY message. The GPIO driver > > > +should serialize messages and determine whether a REPLY message is > > > +required. If a REPLY message is expected but not received within the > > > +specified timeout period (currently 1 second in the Linux driver), > > > +the driver should return -ETIMEOUT. > > > + > > > +GET_DIRECTION (Cmd=2) > > > +~~~~~~~~~~~~~~~~~~~~~ > > > + > > > +**Request:** > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | 2 | line | 0 | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +**Reply:** > > > + > > > +.. code-block:: none > > > + > > > + +------+--------+--------+ > > > + | 0x00 | 0x01 | 0x02 | > > > + | 1 | status | value | > > > + +------+--------+--------+ > > > + > > > +- **status**: > > > + > > > + - 0: Ok > > > + - 1: Error > > > + > > > +- **value**: Direction. > > > + > > > + - 0: None > > > + - 1: Output > > > + - 2: Input > > > + > > > + > > > +SET_DIRECTION (Cmd=3) > > > +~~~~~~~~~~~~~~~~~~~~~ > > > + > > > +**Request:** > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | 3 | line | value | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +- **value**: Direction. > > > + > > > + - 0: None > > > + - 1: Output > > > + - 2: Input > > > + > > > +**Reply:** > > > + > > > +.. code-block:: none > > > + > > > + +------+--------+--------+ > > > + | 0x00 | 0x01 | 0x02 | > > > + | 1 | status | 0 | > > > + +------+--------+--------+ > > > + > > > +- **status**: > > > + > > > + - 0: Ok > > > + - 1: Error > > > + > > > + > > > +GET_VALUE (Cmd=4) > > > +~~~~~~~~~~~~~~~~~ > > > + > > > +**Request:** > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | 4 | line | 0 | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +**Reply:** > > > + > > > +.. code-block:: none > > > + > > > + +------+--------+--------+ > > > + | 0x00 | 0x01 | 0x02 | > > > + | 1 | status | value | > > > + +------+--------+--------+ > > > + > > > +- **status**: > > > + > > > + - 0: Ok > > > + - 1: Error > > > + > > > +- **value**: Level. > > > + > > > + - 0: Low > > > + - 1: High > > > + > > > + > > > +SET_VALUE (Cmd=5) > > > +~~~~~~~~~~~~~~~~~ > > > + > > > +**Request:** > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | 5 | line | value | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +- **value**: Output level. > > > + > > > + - 0: Low > > > + - 1: High > > > + > > > +**Reply:** > > > + > > > +.. code-block:: none > > > + > > > + +------+--------+--------+ > > > + | 0x00 | 0x01 | 0x02 | > > > + | 1 | status | 0 | > > > + +------+--------+--------+ > > > + > > > +- **status**: > > > + > > > + - 0: Ok > > > + - 1: Error > > > + > > > + > > > +SET_IRQ_TYPE (Cmd=6) > > > +~~~~~~~~~~~~~~~~~~~~ > > > + > > > +**Request:** > > > + > > > +.. code-block:: none > > > + > > > + +------+------+------+------+------+------+------+------+ > > > + | 0x00 | 0x01 | 0x02 | 0x03 | 0x04 | 0x05 | 0x06 | 0x07 | > > > + | 6 | line | value | > > > + +------+------+------+------+------+------+------+------+ > > > + > > > +- **value**: IRQ types. > > > + > > > + - 0: Interrupt disabled > > > + - 1: Rising edge trigger > > > + - 2: Falling edge trigger > > > + - 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? > > 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"? > > > > > + > > > +**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 > > >
