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Date:   Mon, 14 Jun 2021 14:54:22 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Cc:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        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>,
        Alex =?utf-8?Q?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>
Subject: Re: [PATCH V3 1/3] gpio: Add virtio-gpio driver
Message-ID: <20210614092422.jmq2i3vlkjmy6cvf@vireshk-i7>
References: <cover.1623326176.git.viresh.kumar@linaro.org>
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 <CACRpkdZV2v2S5z7CZf_8DV=At9-oPSj7RYFH78hWy3ZX37QnDQ@mail.gmail.com>
 <20210611035623.z4f2ynumzozigqnv@vireshk-i7>
 <CAMuHMdVrtSnFpPbB0P3Wxqm1D6vU1_cnh3ypsZJRNF6ueKdAsw@mail.gmail.com>
 <db2d29fd-ff27-0c75-2472-dd031564dbf1@metux.net>
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On 14-06-21, 10:03, Enrico Weigelt, metux IT consult wrote:
> 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

Interesting, so this is a qemu-specific backend you have here.

The way we are looking to write the backend (in Project Stratos at
Linaro) is to make it hypervisor agnostic. So any hypervisor that
understands the vhost protocol can use our backend without changing a
single line of code. The backend will not be part of any
hypervisor's/VMM's source code. FWIW, this doesn't add anything
special to the virtio protocol (like GPIO).

Here is a C based backend we have for I2C:

https://yhbt.net/lore/all/cover.1617278395.git.viresh.kumar@linaro.org/T/#m3b5044bad9769b170f505e63bd081eb27cef8db2

I started with keeping code in QEMU itself but now replaced it with
one in RUST.

https://github.com/vireshk/vhost-device/tree/master/src/i2c

-- 
viresh