linux-kernel - Re: [PATCH v4 1/8] ASoC: dt-bindings: fsl_asrc: Change asrc-width to asrc-format

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Date:   Mon, 2 Mar 2020 23:37:46 -0800
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Rob Herring <robh@...nel.org>,
        Shengjiu Wang <shengjiu.wang@....com>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        linuxppc-dev@...ts.ozlabs.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        shawnguo@...nel.org, s.hauer@...gutronix.de,
        Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-imx@....com,
        kernel@...gutronix.de, Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/8] ASoC: dt-bindings: fsl_asrc: Change asrc-width to
 asrc-format

On Tue, Mar 03, 2020 at 11:59:30AM +0800, Shengjiu Wang wrote:
> Hi
> 
> On Tue, Mar 3, 2020 at 9:43 AM Rob Herring <robh@...nel.org> wrote:
> >
> > On Sun, Mar 01, 2020 at 01:24:12PM +0800, Shengjiu Wang wrote:
> > > asrc_format is more inteligent, which is align with the alsa
> > > definition snd_pcm_format_t, we don't need to convert it to
> > > format in driver, and it can distinguish S24_LE & S24_3LE.
> > >
> > > Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> > > ---
> > >  Documentation/devicetree/bindings/sound/fsl,asrc.txt | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/sound/fsl,asrc.txt b/Documentation/devicetree/bindings/sound/fsl,asrc.txt
> > > index cb9a25165503..0cbb86c026d5 100644
> > > --- a/Documentation/devicetree/bindings/sound/fsl,asrc.txt
> > > +++ b/Documentation/devicetree/bindings/sound/fsl,asrc.txt
> > > @@ -38,7 +38,9 @@ Required properties:
> > >
> > >     - fsl,asrc-rate   : Defines a mutual sample rate used by DPCM Back Ends.
> > >
> > > -   - fsl,asrc-width  : Defines a mutual sample width used by DPCM Back Ends.
> > > +   - fsl,asrc-format : Defines a mutual sample format used by DPCM Back
> > > +                       Ends. The value is one of SNDRV_PCM_FORMAT_XX in
> > > +                       "include/uapi/sound/asound.h"
> >
> > You can't just change properties. They are an ABI.
> 
> I have updated all the things related with this ABI in this patch series.
> What else should I do?

You probably should add one beside the old one. And all
the existing drivers would have to continue to support
"fsl,asrc-width", even if they start to support the new
"fsl,asrc-format". The ground rule here is that a newer
kernel should be able to work with an old DTB, IIRC.

One more concern here is about the format value. Though
I don't think those values, defined in asound.h, would
be changed, yet I am not sure if it's legit to align DT
bindings to a subsystem header file -- I only know that
usually we keep shared macros under include/dt-bindings
folder. I won't have any problem, if either Rob or Mark
has no objection.