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

[Daniel Baluta]

On Tue, Jul 30, 2019 at 10:59 AM Nicolin Chen <nicoleotsuka@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx> 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?

Tested on imx6sx-sdb, everything looks good. No bus errors.