Date: Tue, 26 Apr 2016 12:15:32 +0100
From: Peter Griffin <peter.griffin@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        srinivas.kandagatla@gmail.com, maxime.coquelin@st.com,
        patrice.chotard@st.com, vinod.koul@intel.com, lee.jones@linaro.org,
        dmaengine@vger.kernel.org, devicetree@vger.kernel.org,
        broonie@kernel.org, ludovic.barre@st.com, arnaud.pouliquen@st.com
Subject: Re: [PATCH 09/18] ASoC: sti: Update DT example to match the driver
 code
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Hi Arnd,

On Tue, 26 Apr 2016, Arnd Bergmann wrote:

> On Tuesday 26 April 2016 11:11:36 Peter Griffin wrote:
> > Hi Arnd,
> > 
> > On Thu, 21 Apr 2016, Arnd Bergmann wrote:
> > 
> > > On Thursday 21 April 2016 12:04:26 Peter Griffin wrote:
> > > > uniperiph-id, version and mode are ST specific bindings and
> > > > need the 'st,' prefix. Update the examples, as otherwise copying
> > > > them yields a runtime error parsing the DT node.
> > > > 
> > > > Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> > > > Cc: arnaud.pouliquen@st.com
> > > > ---
> > > >  .../devicetree/bindings/sound/st,sti-asoc-card.txt         | 14 +++++++-------
> > > >  1 file changed, 7 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/sound/st,sti-asoc-card.txt b/Documentation/devicetree/bindings/sound/st,sti-asoc-card.txt
> > > > index 028fa1c..ef2e0c6 100644
> > > > --- a/Documentation/devicetree/bindings/sound/st,sti-asoc-card.txt
> > > > +++ b/Documentation/devicetree/bindings/sound/st,sti-asoc-card.txt
> > > > @@ -67,9 +67,9 @@ Example:
> > > >                 dmas = <&fdma0 4 0 1>;
> > > >                 dai-name = "Uni Player #1 (DAC)";
> > > >                 dma-names = "tx";
> > > > -               uniperiph-id = <2>;
> > > > -               version = <5>;
> > > > -               mode = "PCM";
> > > > +               st,uniperiph-id = <2>;
> > > > +               st,version = <5>;
> > > > +               st,mode = "PCM";
> > > >         };
> > > 
> > > You don't change the binding desciption here, only the example,
> > > so they no longer match.
> > 
> > Whoops. Will fix that in v4.
> > 
> > > 
> > > What is st,uniperiph-id needed for anyway? It's often an indication
> > > that you are doing something wrong if you need this.
> > 
> > From looking at the code in sound/soc/sti/uniperif_player.c, there is
> > one sysconf register called "Audio glue config" which is shared by all
> > of the uniperif IP instances. This binding is being used to generate a
> > bitoffset into this shared register based on the instance of the IP.
> > 
> > I guess the alternative is to have an explosion of compatibles?
> > 
> > st,sti-uni-player-1
> > st,sti-uni-player-2
> > st,sti-uni-player-3
> > 
> 
> That would certainly be worse: if the devices are actually identical,
> they should have the same compatible string.
> 
> > If not what would you recommend instead? :-)
> 
> It's still not clear to me what that bit in the syscfg register
> is for. Given the error message about "sti-audio-clk-glue",
> I suspect that this is actually a clock controller and that
> it should be using the clock binding with a separate driver
> instead of manipulating the regmap directly from the audio driver.

Luckily I do have the datasheet for the audio-glue sysconf register.

It says: -

[11:8] PCM_CLK_SEL: Selects the frequency synthesizer clock or the external
PCM clock for each channel.

The driver only ever sets this to 1 which selects the frequency synthesizer
clock. So the bitfield of the register which the driver is using (PCM_CLK_SEL)
is a clock mux.

Peter.