linux-kernel - Re: [PATCH 1/5] mfd: lochnagar: Add support for the Cirrus Logic Lochnagar

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Message-ID: <20180917135016.GK1653@imbe.wolfsonmicro.main>
Date:   Mon, 17 Sep 2018 14:50:16 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Rob Herring <robh@...nel.org>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH 1/5] mfd: lochnagar: Add support for the Cirrus Logic
 Lochnagar

On Sun, Sep 16, 2018 at 06:11:08PM -0500, Rob Herring wrote:
> On Thu, Sep 06, 2018 at 03:48:34PM +0100, Charles Keepax wrote:
> > On Thu, Sep 06, 2018 at 03:46:12PM +0200, Linus Walleij wrote:
> > > On Wed, Sep 5, 2018 at 12:41 PM Charles Keepax
> > > <ckeepax@...nsource.cirrus.com> wrote:
> > > It's a bit confusing, maybe you can clear it up:
> > > it appears to be an I2C device, so when you say this is a
> > > "development board" is there something like a board
> > > controller that is accessed over I2C and this is what the
> > > driver really probes to, not the board per se?
> > > 
> > > I guess jamming this card into the I2C slot of any other
> > > system (would work fine with a 96Boards LS connector
> > > as it seems, actually)  also involves connecting some
> > > I2S or similar on the side for high-datarate traffic?
> > > 
> > > This driver seems to only concern itself with the I2C
> > > board controller per se, not the board is that right?
> > > 
> > 
> > Yeah I have poorly phrased that, these patches are very much
> > just dealing with the board controller chip.
> 
> How would the codec I2C connect to the host? Is there one I2C bus or 
> 2? The binding looks mostly fine to me, but I think we need to 
> understand that part.
> 

If the CODEC is I2C based then both the CODEC and the controller
IC will be on the same I2C bus. If the CODEC is connected over
SPI that is obviously a separate bus as the board controller
chip is I2C only.

There are some additional I2C interfaces but they are not
currently used on any mini-cards, and they are intended for
secondary purposes not control of the CODEC itself.

Thanks,
Charles