[RFC SOF 1/2] topology: Add sof-byt-codec-tdm4.m4 file

[Hans de Goede]

Hi,

On 12/7/20 4:11 PM, Pierre-Louis Bossart wrote:
> Hi Hans,
> 
>> Some BYT/CHT boards (mostly Cherry Trail) use TDM 4 slots 24 bit as
>> wire format to the codec, rather then standard I2S 2 channel 24 bit.
>>
>> Add a new m4 file for this. This is a copy of sof-byt-codec.m4 with
>> the following changes:
>>
>> @@ -1,4 +1,4 @@
>> -`# Topology for generic' PLATFORM `board with' CODEC `on SSP' SSP_NUM
>> +`# Topology for generic' PLATFORM `board with' CODEC `on SSP' SSP_NUM `using TDM 4 slots 24 bit'
>>
>>   # Include topology builder
>>   include(`utils.m4')
>> @@ -97,8 +97,8 @@
>>   # BE configurations - overrides config in ACPI if present
>>   #
>>   DAI_CONFIG(SSP, SSP_NUM, 0, SSP2-Codec,
>> -       SSP_CONFIG(I2S, SSP_CLOCK(mclk, 19200000, codec_mclk_in),
>> -              SSP_CLOCK(bclk, 2400000, codec_slave),
>> +       SSP_CONFIG(DSP_B, SSP_CLOCK(mclk, 19200000, codec_mclk_in),
>> +              SSP_CLOCK(bclk, 4800000, codec_slave),
>>                 SSP_CLOCK(fsync, 48000, codec_slave),
>> -              SSP_TDM(2, 25, 3, 3),
>> +              SSP_TDM(4, 25, 3, 3),
>>                 SSP_CONFIG_DATA(SSP, SSP_NUM, 24)))
> 
> I don't think this change is necessary, the problem is probably that we still rely on the hard-coded 4 slots in the machine driver which was the default for the Atom/SST driver.
> 
> If I look at the cht_bsw_nau8824.c driver, the only place where there is a reference to 4 slots is in the cht_codec_init() function.
> 
> https://elixir.bootlin.com/linux/latest/source/sound/soc/intel/boards/cht_bsw_nau8824.c#L104
> 
> In other drivers, this was moved to the codec_fixup routine which is overridden/ignored when SOF is used.
> 
> see e.g.
> 
> https://elixir.bootlin.com/linux/latest/source/sound/soc/intel/boards/cht_bsw_max98090_ti.c
> 
> https://elixir.bootlin.com/linux/latest/source/sound/soc/intel/boards/cht_bsw_rt5645.c
> 
> If you follow the same pattern that should make this problem go away. When SOF is used we typically don't have any hard-coded format and whatever is defined in the topology is propagated to the codec driver.

As I explained in the cover, this effectively switches to I2S 2 channel 24 bit format,
which requires mixer-setting / UCM changes in case of the nau8824 codec. The codec
driver has this comment:

 * Configures a DAI for TDM operation. Only support 4 slots TDM.
 */
static int nau8824_set_tdm_slot(struct snd_soc_dai *dai,
        unsigned int tx_mask, unsigned int rx_mask, int slots, int slot_width)

Which is not entirely true I did get playback to work with I2S 2 channel 24 bit
(I did not test recording yet) but playback only works after mixer setting
changes, which in turn break things under SST.

Please read the cover letter, which should explain the issue.

As mentioned there we could use I2S 2 channel 24 bit as we do everywhere
(I like standardizing on that) but then the UCM profile would need to
differentiate between the SST and SOF setups and adjust the mixer
accordingly to not regress SST setups.

Regards,

Hans