linux-kernel - Re: [PATCH v8] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <20210319054035.47tn747lkagpip6v@vireshk-i7>
Date:   Fri, 19 Mar 2021 11:10:35 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Jie Deng <jie.deng@...el.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        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>,
        Wolfram Sang <wsa@...nel.org>,
        Jason Wang <jasowang@...hat.com>,
        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,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v8] i2c: virtio: add a virtio i2c frontend driver

On 19-03-21, 13:31, Jie Deng wrote:
> 
> On 2021/3/19 11:54, Viresh Kumar wrote:
> > On 18-03-21, 15:52, Arnd Bergmann wrote:
> > > Allowing multiple virtio-i2c controllers in one system, and multiple i2c
> > > devices attached to each controller is clearly something that has to work.
> > Good.
> > 
> > > I don't actually see a limitation though. Viresh, what is the problem
> > > you see for having multiple controllers?
> > I thought this would be a problem in that case as we are using the global
> > virtio_adapter here.
> > 
> > +       vi->adap = &virtio_adapter;
> > +       i2c_set_adapdata(vi->adap, vi);
> > 
> > Multiple calls to probe() will end up updating the same pointer inside adap.
> > 
> > +       vi->adap->dev.parent = &vdev->dev;
> > 
> > Same here, overwrite.
> > 
> > +       /* Setup ACPI node for controlled devices which will be probed through ACPI */
> > +       ACPI_COMPANION_SET(&vi->adap->dev, ACPI_COMPANION(pdev));
> > +       vi->adap->timeout = HZ / 10;
> > 
> > These may be fine, but still not ideal I believe.
> > 
> > +       ret = i2c_add_adapter(vi->adap);
> > i
> > This should be a problem as well, we must be adding this to some sort of list,
> > doing some RPM stuff, etc ?
> > 
> > Jie, the solution is to allocate memory for adap at runtime in probe and remove
> > the virtio_adapter structure completely.
> 
> 
> If you want to support that. Then I think we don't need to change the
> following at all.
> 
> > +    .algo = &virtio_algorithm,
> > +
> > +        return ret;
> > +
> > +    vi->adap = virtio_adapter;
> This is strange, why are you allocating memory for adapter twice ?
> Once for virtio_adapter and once for vi->adap ? Either fill the fields
> directly for v->adap here and remove virtio_adapter or make vi->adap a
> pointer.

Yes, your previous version was partly okay but you don't need the
virtio_algorithm structure to be allocated. There are only 4 fields you are
updating here, just fill them directly in vi->adap.

(FWIW, I also suggested the same when I said
"Either fill the fields directly for v->adap here and remove virtio_adapter".
)

See how drivers/i2c/busses/i2c-versatile.c and most of the other drivers have
done it.

-- 
viresh