linux-kernel - Re: [alsa-devel] [PATCH v2 1/7] ASoC: fsl_sai: Add registers definition for multiple datalines

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Date:   Tue, 30 Jul 2019 00:59:35 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Daniel Baluta <daniel.baluta@...il.com>,
        Daniel Baluta <daniel.baluta@....com>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Timur Tabi <timur@...nel.org>, Rob Herring <robh@...nel.org>,
        "S.j. Wang" <shengjiu.wang@....com>,
        "Angus Ainslie (Purism)" <angus@...ea.ca>,
        Takashi Iwai <tiwai@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Viorel Suman <viorel.suman@....com>,
        Fabio Estevam <festevam@...il.com>,
        Mihai Serban <mihai.serban@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>
Subject: Re: [alsa-devel] [PATCH v2 1/7] ASoC: fsl_sai: Add registers
 definition for multiple datalines

On Mon, Jul 29, 2019 at 09:20:01PM +0100, Mark Brown wrote:
> On Mon, Jul 29, 2019 at 10:57:43PM +0300, Daniel Baluta wrote:
> > On Mon, Jul 29, 2019 at 10:42 PM Nicolin Chen <nicoleotsuka@...il.com> wrote:
> > > On Sun, Jul 28, 2019 at 10:24:23PM +0300, Daniel Baluta wrote:
> 
> > > > @@ -704,7 +711,14 @@ static bool fsl_sai_readable_reg(struct device *dev, unsigned int reg)
> > > >       case FSL_SAI_TCR3:
> > > >       case FSL_SAI_TCR4:
> > > >       case FSL_SAI_TCR5:
> > > > -     case FSL_SAI_TFR:
> > > > +     case FSL_SAI_TFR0:
> 
> > > A tricky thing here is that those SAI instances on older SoC don't
> > > support multi data lines physically, while seemly having registers
> > > pre-defined. So your change doesn't sound doing anything wrong to
> > > them at all, I am still wondering if it is necessary to apply them
> > > to newer compatible only though, as for older compatibles of SAI,
> > > these registers would be useless and confusing if being exposed.
> 
> > > What do you think?
> 
> > Yes, I thought about this too. But, I tried to keep the code as short
> > as possible and technically it is not wrong. When 1 data line is supported
> > for example application will only care about TDR0, TFR0, etc.
> 
> So long as it's safe to read the registers (you don't get a bus error or
> anything) I'd say it's more trouble than it's worth to have separate
> regmap configuations just for this.  The main reasons for restricting
> readability are where there's physical problems with doing the reads or
> to keep the size of the debugfs files under control for usability and
> performance reasons.

Thanks for the input, Mark.

Daniel, did you get a chance to test it on older SoCs? At least
nothing breaks like bus errors?