linux-kernel - Re: [PATCH v1] i2c: npcm7xx: Support changing bus speed using debugfs.

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Message-ID: <CAKKbWA4gHobXFGi5CiPnawWoMOi0GFrCbzanuOFZ+Aky6=9Mpg@mail.gmail.com>
Date:   Thu, 1 Oct 2020 20:13:49 +0300
From:   Avi Fishman <avifishman70@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Tali Perry <tali.perry1@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Wolfram Sang <wsa@...nel.org>, Alex Qiu <xqiu@...gle.com>,
        Kun Yi <kunyi@...gle.com>,
        Benjamin Fair <benjaminfair@...gle.com>,
        Joel Stanley <joel@....id.au>,
        Tomer Maimon <tmaimon77@...il.com>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] i2c: npcm7xx: Support changing bus speed using debugfs.

Hi Andy,

Customers using BMC with complex i2c topology asked us to support
changing bus frequency at run time, for example same device will
communicate with one slave at 100Kbp/s and another with 400kbp/s and
maybe also with smae device at different speed (for example an i2c
mux).
This is not only for debug.
Can DT overlay support that?

On Thu, Oct 1, 2020 at 6:40 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Thu, Oct 1, 2020 at 8:34 AM Tali Perry <tali.perry1@...il.com> wrote:
> > On Wed, Sep 30, 2020 at 12:31 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > > On Wed, Sep 30, 2020 at 10:13:42AM +0300, Tali Perry wrote:
> > > > Systems that can dinamically add and remove slave devices
> > >
> > > dynamically
> > >
> > > > often need to change the bus speed in runtime.
> > >
> > > > This patch exposes the bus frequency to the user.
> > >
> > > Expose the bus frequency to the user.
> > >
> > > > This feature can also be used for test automation.
> > >
> > > In general I think that DT overlays or so should be user rather than this.
> > > If we allow to change bus speed settings for debugging purposes it might make
> > > sense to do this on framework level for all drivers which support that (via
> > > additional callback or so).
> >
> > Do you mean adding something like this:
>
> Nope. I meant to use DT description for that. I²C core should cope
> with DT already.
> I do not understand why you need special nodes for that rather than DT
> overlay which will change the speed for you.
>
> --
> With Best Regards,
> Andy Shevchenko



-- 
Regards,
Avi