[alsa-devel] [Q] ASoC: What's the real meaning of SND_SOC_DAIFMT_NB_NF?

[javier Martin]

On 24 February 2012 09:34, Peter Ujfalusi <peter.ujfalusi at ti.com> wrote:
> On 02/24/2012 09:53 AM, javier Martin wrote:
>> If TFSI bit is 1, frame clock is active high.
>> If TFSI bit is 0, frame clock is active low.
>>
>> In the piece of code I've shown to you, when someone configures
>> (SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF) he's really selecting an
>> active high frame clock when the standard says just the opposite
>> (wm8974 datasheet p50).
>
> We had similar issues on OMAP McBSP in the past. If you take a look at
> the omap-mcbsp.c: omap_mcbsp_dai_set_dai_fmt() function we have inv_fs
> variable to handle such a case.
> We do the FS/BCLK configuration only in DAIFMT_INV config phase. The FS
> active level is different in these formats. We invert the FS based on
> the used format (LEFT/RIGHT just, DSP). The DAIFMT_INV switch configures
> according to I2S, but we invert the FS if we are in DSP, Justified modes
> afterwards.

I intend to do something similar for imx-ssi. What keeps me awake is
that there are some other platforms as well that don't respect the
convention.

>>>> there is at least one platform relying on this misleading behavior
>>>> that I can't test:
>>>> http://lxr.linux.no/#linux+v3.2.7/sound/soc/imx/wm1133-ev1.c#L81
>>>
>>> That was correct at the time it was written, though the code has changed
>>> since then and I don't know when it was last retested.  Of course
>>> depending on the signal it may interoperate well even if the setup isn't
>>> actually correct.  I'd just fix the driver and if it works for yours
>>> it's probably OK for that board too.
>>
>> It is not one but two boards that are affected:
>> http://lxr.linux.no/#linux+v3.2.7/sound/soc/imx/wm1133-ev1.c#L81
>> http://lxr.linux.no/#linux+v3.2.7/sound/soc/imx/eukrea-tlv320.c#L32
>>
>> If I fixed the bug in the SSI I would break both of them, since I
>> would be changing frame clock polarity.
>
> I don't think it is going to break. I would guess that the channels are
> swapped on these machines at the moment. If you correct the CPU dai
> driver the only thing that will happen is that the channels will jump in
> their correct place.

That would be true for stereo. However, mono should not be working right now.

-- 
Javier Martin
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