[RESEND] drm/i2c: tda998x: Reset the I2S_FORMAT (Page0, Reg 0xfc) to it's default

[Russell King - ARM Linux admin]

On Fri, Feb 22, 2019 at 03:27:43PM +0000, Russell King - ARM Linux admin wrote:
> On Fri, Feb 22, 2019 at 05:20:15PM +0200, Peter Ujfalusi wrote:
> > Hi Russell,
> > 
> > On 22/02/2019 16.35, Russell King - ARM Linux admin wrote:
> > > It would also be good to know what Fs value(s) BBB uses, and what
> > > sample sizes you have tested.
> > 
> > On BBB McASP is the clock master and as I recall I have tested 44.1, 48
> > KHz at least with 16 and 24 bits.
> 
> Sorry, I wasn't clear enough... is the bus clocked at 32Fs for 16bit
> samples and 64Fs for 24bit samples, or is it 64Fs for both?

To be clear, the reason I'm asking for this information is that
Sven Van Asbroeck is trying to use TDA998x, and he has a problem with
the current implementation that adjusts CTS_N_M and CTS_N_K parameters
according to the _sample_ size.

This appears to be wrong, these settings should be set according to
the BCLK ratio (Fs multiplier) and not the sample size.

If you say that the existing code works for you, but your device
always produces a bclk at 64fs, then we have a problem - it means
that to add support for Sven's platform, we're probably going to end
up causing a regression for your platform.

The next issue is with snd_soc_dai_set_bclk_ratio().  Today, no one
calls that function, so none of the DAI .set_bclk_ratio
implementations are used (and probably completely untested.)  If your
CPU DAI changes the bclk ratio depending on the sample size, I will
need something to call that function at the appropriate time to set
the clocking ratio.

I suspect most codecs don't care about it, but TDA998x does, because
it _looks_ like it uses the BCLK to generate the CTS value to be
passed to the HDMI sink.  Since CTS = f(tmds) * N / (128 * fs),
using BCLK to derive the CTS value requires TDA998x to know the
BCLK ratio.

So, knowing this information ahead of time is very advantageous.

-- 
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