linux-kernel - Re: [PATCH v2 2/4] dt-bindings: add bus number property

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Date:   Tue, 5 Oct 2021 18:22:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Paweł Anikiel <pan@...ihalf.com>
Cc:     jarkko.nikula@...ux.intel.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        SoC Team <soc@...nel.org>, Dinh Nguyen <dinguyen@...nel.org>,
        Pratyush Yadav <p.yadav@...com>,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Sebastian Reichel <sre@...nel.org>,
        "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        ka@...ihalf.com, Tomasz Nowicki <tn@...ihalf.com>,
        jam@...ihalf.com, amstan@...gle.com
Subject: Re: [PATCH v2 2/4] dt-bindings: add bus number property

On Tue, Oct 5, 2021 at 4:37 PM Paweł Anikiel <pan@...ihalf.com> wrote:
>
> On SoCFPGA systems, it's desireable to have fixed numbering for
> i2c busses, while being able to enable/disable them (e.g. have i2c1
> be mapped to /dev/i2c-1, even though i2c0 is disabled). This can also
> be achieved using devicetree aliases (see i2c_add_adapter). However,
> having the driver be self-contained without relying on aliases is more
> robust.
>
> Signed-off-by: Paweł Anikiel <pan@...ihalf.com>

I don't see how adding a nonstandard property in one of the i2c bus
drivers helps at all. How do you expect this to work when there are
multiple i2c controllers in the system using different drivers? What
should happen if both an alias and the busno property are set?

      Arnd