[PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver

Thu Apr 30 00:35:09 PDT 2026

Hello,

On 4/29/26 21:20, Mathieu Poirier wrote:
> On Wed, 29 Apr 2026 at 12:07, Padhi, Beleswar <b-padhi at ti.com> wrote:
>>
>> Hi Mathieu,
>>
>> On 4/29/2026 11:03 PM, Mathieu Poirier wrote:
>>> On Wed, 29 Apr 2026 at 10:53, Shenwei Wang <shenwei.wang at nxp.com> wrote:
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Mathieu Poirier <mathieu.poirier at linaro.org>
>>>>> Sent: Wednesday, April 29, 2026 10:42 AM
>>>>> To: Shenwei Wang <shenwei.wang at nxp.com>
>>>>> Cc: Andrew Lunn <andrew at lunn.ch>; Padhi, Beleswar <b-padhi at ti.com>; Linus
>>>>> Walleij <linusw at kernel.org>; Bartosz Golaszewski <brgl at kernel.org>; Jonathan
>>>>> Corbet <corbet at lwn.net>; Rob Herring <robh at kernel.org>; Krzysztof Kozlowski
>>>>> <krzk+dt at kernel.org>; Conor Dooley <conor+dt at kernel.org>; Bjorn Andersson
>>>>> <andersson at kernel.org>; Frank Li <frank.li at nxp.com>; Sascha Hauer
>>>>> <s.hauer at pengutronix.de>; Shuah Khan <skhan at linuxfoundation.org>; linux-
>>>>> gpio at vger.kernel.org; linux-doc at vger.kernel.org; linux-kernel at vger.kernel.org;
>>>>> Pengutronix Kernel Team <kernel at pengutronix.de>; Fabio Estevam
>>>>> <festevam at gmail.com>; Peng Fan <peng.fan at nxp.com>;
>>>>> devicetree at vger.kernel.org; linux-remoteproc at vger.kernel.org;
>>>>> imx at lists.linux.dev; linux-arm-kernel at lists.infradead.org; dl-linux-imx <linux-
>>>>> imx at nxp.com>; Bartosz Golaszewski <brgl at bgdev.pl>
>>>>> Subject: [EXT] Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
>>>>> On Tue, Apr 28, 2026 at 03:24:59PM +0000, Shenwei Wang wrote:
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: Andrew Lunn <andrew at lunn.ch>
>>>>>>> Sent: Monday, April 27, 2026 3:49 PM
>>>>>>> To: Shenwei Wang <shenwei.wang at nxp.com>
>>>>>>> Cc: Padhi, Beleswar <b-padhi at ti.com>; Linus Walleij
>>>>>>> <linusw at kernel.org>; Bartosz Golaszewski <brgl at kernel.org>; Jonathan
>>>>>>> Corbet <corbet at lwn.net>; Rob Herring <robh at kernel.org>; Krzysztof
>>>>>>> Kozlowski <krzk+dt at kernel.org>; Conor Dooley <conor+dt at kernel.org>;
>>>>>>> Bjorn Andersson <andersson at kernel.org>; Mathieu Poirier
>>>>>>> <mathieu.poirier at linaro.org>; Frank Li <frank.li at nxp.com>; Sascha
>>>>>>> Hauer <s.hauer at pengutronix.de>; Shuah Khan
>>>>>>> <skhan at linuxfoundation.org>; linux-gpio at vger.kernel.org; linux-
>>>>>>> doc at vger.kernel.org; linux-kernel at vger.kernel.org; Pengutronix
>>>>>>> Kernel Team <kernel at pengutronix.de>; Fabio Estevam
>>>>>>> <festevam at gmail.com>; Peng Fan <peng.fan at nxp.com>;
>>>>>>> devicetree at vger.kernel.org; linux- remoteproc at vger.kernel.org;
>>>>>>> imx at lists.linux.dev; linux-arm- kernel at lists.infradead.org;
>>>>>>> dl-linux-imx <linux-imx at nxp.com>; Bartosz Golaszewski
>>>>>>> <brgl at bgdev.pl>
>>>>>>> Subject: [EXT] Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg
>>>>>>> GPIO driver
>>>>>>>>> struct virtio_gpio_response {
>>>>>>>>>           __u8 status;
>>>>>>>>>           __u8 value;
>>>>>>>>> };
>>>>>>>> It is the same message format. Please see the message definition
>>>>>>> (GET_DIRECTION) below:
>>>>>>>
>>>>>>>> +   +-----+-----+-----+-----+-----+----+
>>>>>>>> +   |0x00 |0x01 |0x02 |0x03 |0x04 |0x05|
>>>>>>>> +   | 1   | 2   |port |line | err | dir|
>>>>>>>> +   +-----+-----+-----+-----+-----+----+
>>>>>>> Sorry, but i don't see how two u8 vs six u8 are the same message format.
>>>>>>>
>>>>>> Some changes to the message format are necessary.
>>>>>>
>>>>>> Virtio uses two communication channels (virtqueues): one for requests and
>>>>> replies, and a second one for events.
>>>>>> In contrast, rpmsg provides only a single communication channel, so a
>>>>>> type field is required to distinguish between different kinds of messages.
>>>>>>
>>>>>> Since rpmsg replies and events share the same message format, an additional
>>>>> line is introduced to handle both cases.
>>>>>> Finally, rpmsg supports multiple GPIO controllers, so a port field is added to
>>>>> uniquely identify the target controller.
>>>>>
>>>>> I have commented on this before - RPMSG is already providing multiplexing
>>>>> capability by way of endpoints.  There is no need for a port field.  One endpoint,
>>>>> one GPIO controller.
>>>>>
>>>> You still need a way to let the remote side know which port the endpoint maps to, either
>>>> by embedding the port information in the message (the current way), or by sending it
>>>> separately.
>>>>
>>> An endpoint is created with every namespace request.  There should be
>>> one namespace request for every GPIO controller, which yields a unique
>>> endpoint for each controller and eliminates the need for an extra
>>> field to identify them.
>>
>>
>> Right, but this can still be done by just having one namespace request.
>> We can create new endpoints bound to an existing namespace/channel by
>> invoking rpmsg_create_ept(). This is what I suggested here too:
>> https://lore.kernel.org/all/29485742-6e49-482e-b73d-228295daaeec@ti.com/
>>
> 
> I will look at your suggestion (i.e link above) later this week or next week.
> 
>> My mental model looks like this for the complete picture:
>>
>> 1. namespace/channel#1 = rpmsg-io
>>      a. ept1 -> gpio-controller at 1
>>      b. ept2 -> gpio-controller at 2
>>
> 
> I've asked for one endpoint per GPIO controller since the very
> beginning.  I don't yet have a strong opinion on whether to use one
> namespace request per GPIO controller or a single request that spins
> off multiple endpoints.  I'll have to look at your link and reflect on
> that.  Regardless of how we proceed on that front, multiplexing needs
> to happen at the endpoint level rather than the packet level.  This is
> the only way this work can move forward.
> 

I would be more in favor of Mathieu’s proposal: “An endpoint is created 
with every namespace request.”

If the endpoint is created only on the Linux side, how do we match the 
Linux endpoint address with the local port field on the remote side?

With a multi-namespace approach, the namespace could be rpmsg-io-[addr], 
where [addr] corresponds to the GPIO controller address in the DT. This 
would:

- match the RPMsg probe with the DT,
- provide a simple mapping between the port and the endpoint on both sides,
- allow multiple endpoints on the remote side,
- provide a simple discovery mechanism for remote capabilities.

Regards,
Arnaud

>> 2. namespace/channel#2 = rpmsg-i2c
>>      a. ept1 -> i2c at 1
>>      b. ept2 -> i2c at 2
>>      c. ept3 -> i2c at 3
>>
>> etc...
>>
>> This way device groups are isolated with each channel/namespace, and
>> instances within each device groups are also respected with specific
>> endpoints.
>>
>> Thanks,
>> Beleswar
>>
> 