linux-kernel - Re: [PATCH V3 1/3] gpio: Add virtio-gpio driver

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Date:   Mon, 21 Jun 2021 12:25:28 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        Viresh Kumar <vireshk@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bill Mills <bill.mills@...aro.org>,
        Alex Benn?e <alex.bennee@...aro.org>,
        stratos-dev@...lists.linaro.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Stefano Garzarella --cc virtualization @ lists . linux-foundation . org" 
        <sgarzare@...hat.com>, virtualization@...ts.linux-foundation.org,
        Alistair Strachan <astrachan@...gle.com>
Subject: Re: [PATCH V3 1/3] gpio: Add virtio-gpio driver

On Wed 16 Jun 10:52 CDT 2021, Enrico Weigelt, metux IT consult wrote:

> On 16.06.21 05:30, Bjorn Andersson wrote:
> 
> > Combined with the virtio-i2c effort this could provide an alternative by
> > simply tunneling the busses and GPIOs into Linux and use standard iio
> > drivers, for cases where this suits your product requirements better.
> 
> So, you wanna use virtio as logical interface between the two CPUs ?
> Interesting idea. Usually folks use rpmsg for those things.
> 

rpmsg is a layer on top of virtio, so this would be an extension of the
existing model.

There's been discussions (and I believe some implementations) related to
bridging I2C requests over rpmsg, but I think it's preferable to
standardize around the virtio based bearer directly.

> What is running on the secondary CPU ? Some OS like Linux or some bare
> metal stuff ? What kind of CPU is that anyways ?
> 

These ideas revolves around platforms that implements something like the
"Android Sensor Hub", which provides some resource constraint
co-processor that deals with sensor device interaction and processing of
the data without waking up the power-hungry ARM cores.

Given the focus on power consumption I would guess that these are not
going to run Linux. Core-wise I've seen this implemented using primarily
ARM and Hexagon cores.

Regards,
Bjorn