linux-kernel - Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <YNrZVho/98qgJS9N@kunai>
Date:   Tue, 29 Jun 2021 10:27:02 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Jie Deng <jie.deng@...el.com>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        conghui.chen@...el.com, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com,
        Sergey Semin <Sergey.Semin@...kalelectronics.ru>,
        Mike Rapoport <rppt@...nel.org>, loic.poulain@...aro.org,
        Tali Perry <tali.perry1@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        yu1.wang@...el.com, shuo.a.liu@...el.com,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver

Hi Viresh,

> While we are at it, this has been replaced by a Rust counterpart [1]
> (as that makes it hypervisor agnostic, which is the goal of my work
> here) and I need someone with I2C knowledge to help review it. It
> should be okay even if you don't understand Rust a lot, just review
> this file[2] which is where most of i2c specific stuff lies.

Can't promise I can do this before my holidays, but I will try.

> I am not sure why you say I2C_RDWR isn't supported. The spec and Linux

This is how I interpreted Arnd's response. I said mulitple times that I
might be missing something so I double check.

> SMBUS. To clarify on an earlier point, every virtio transfer may
> contain one or more struct i2c_msg instances, all processed together
> (as expected).

That was the information missing for me so far becasue...

> If you see virtio_i2c_send_reqs() in this patch, you will see that it
> converts a stream of i2c_req messages to their virtio counterparts and
> send them together, consider it a single transaction.

... when I checked virtio_i2c_send_reqs(), I also saw
virtqueue_add_sgs() but I had no idea if this will end up as REP_START
on the physical bus or not. But it definately should.

Thanks for the pointers!

   Wolfram


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