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

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Date:   Fri, 19 Mar 2021 09:24:35 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        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>,
        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 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.

-- 
viresh