linux-kernel - Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <CAK8P3a0LjcSs7gvU-jRdZJCFrfxQcSUWqL_fgH_71VjC027M0w@mail.gmail.com>
Date:   Mon, 15 Mar 2021 08:52:53 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Jie Deng <jie.deng@...el.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Wolfram Sang <wsa@...nel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.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,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver

On Mon, Mar 15, 2021 at 6:54 AM Jie Deng <jie.deng@...el.com> wrote:
> On 2021/3/15 11:13, Jason Wang wrote:
> > On 2021/3/15 9:14 上午, Jie Deng wrote:
> >> On 2021/3/12 16:58, Arnd Bergmann wrote:
> >
> Then do you think it is necessary to mark the virtio bufs with
> ____cacheline_aligned ?

I think so, yes.

> I haven't seen any virtio interface being marked yet. If this is a
> problem, I believe it should  be common for all virtio devices, right ?

Yes, but it's not a problem if the buffers are allocated separately
because kmalloc provinces a cachelinen aligned buffer on architectures
that need it.

It's only a problem here because there is a single allocation for three
objects that have different ownership states during the DMA (device
owned to-device, cpu-owned, device owned to-cpu).

       Arnd