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Subject: Re: [PATCH V3 1/3] gpio: Add virtio-gpio driver
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        "Enrico Weigelt, metux IT consult" <info@metux.net>,
        Viresh Kumar <vireshk@kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Bill Mills <bill.mills@linaro.org>,
        =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>,
        stratos-dev@op-lists.linaro.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        "Stefano Garzarella --cc virtualization @ lists . linux-foundation . org" 
        <sgarzare@redhat.com>, virtualization@lists.linux-foundation.org,
        Alistair Strachan <astrachan@google.com>
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From:   "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Message-ID: <db2d29fd-ff27-0c75-2472-dd031564dbf1@metux.net>
Date:   Mon, 14 Jun 2021 10:03:42 +0200
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On 11.06.21 09:42, Geert Uytterhoeven wrote:

hi,

> I my PoC "[PATCH QEMU v2 0/5] Add a GPIO backend"[1], I didn't have
> a virtio transport, but just hooked into the PL061 GPIO emulation
> in QEMU.  The PL061 QEMU driver talked to the GPIO backend, which
> talked to /dev/gpiochipN on the host.

for qemu side you might be interested in my patch queue from last year
(including the virtio-gpio implementation) - it also introduces an
gpio backend subsys that allows attaching simulation gpio's to various
backends. so far just implemented a dummy backend (that can be
manipulated by qemu console) and using it just in the virtio-gpio
device emulation.

https://github.com/oss-qm/qemu/tree/wip/gpio-v2

> So QEMU has to translate the virtio-gpio communication to e.g.
> /dev/gpiochipN on the host (or a different backend on non-Linux or
> bare-metal HV).

For qemu case, yes, depending on your actual configuration. You can
attach the virtual device to any gpio backend you like (once it's 
actually implemented). Yet only implemented the dummy, which doesn't
speak to a real hosts gpio, but can be used simulations like HIL.


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@metux.net -- +49-151-27565287