[PATCH 01/38] ASoC: soc-component: Add comment for the endianness flag

[Kirill Marinushkin]

Hello Charles,

In the [PATCH 00/38] of this patch set, you write:

 > 2) Devices behind non-audio buses, SPI just moves bits and doesn't
 > really define an endian for audio data on the bus. Thus it seems the
 > CODEC probably can care about the endian. The only devices that fall
 > into this group (mostly for AoV) are: rt5514-spi.c, rt5677-spi.c,
 > cros_ec_codec.c (only the AoV).

 From my experience with some PCM codecs by TI, they can not care about the

endianness. For example, in driver [1], if I allow BE format as well, 
and configure

the sound card to use BE, it will not work. I have no sound with BE.

In these cases, the codec HW supports *only* LE. That's why their 
`snd_soc_dai_driver`

structures provide only LE in the `format` field.

If such drivers specify `endianness = 1`, then `soc-core` will extend 
their supported

formats with BE counter-parts, see [2]. AFAIU, it will have the same 
effect, as if the

drivers themselves provided their formats in both LE | BE.


I don't think adding `endianness = 1` to such codecs will work as expected.

Unfortunately, I don't have an easy access to HW today, to confirm or 
disprove

this understanding.


Best regards,

Kirill

---

[1] 
https://elixir.bootlin.com/linux/latest/source/sound/soc/codecs/pcm3060.c#L189

[2] 
https://elixir.bootlin.com/linux/latest/source/sound/soc/soc-core.c#L2540


On 5/4/22 7:08 PM, Charles Keepax wrote:
> Add a comment to make the purpose of the endianness flag on the
> snd_soc_component structure more clear.
>
> Signed-off-by: Charles Keepax <ckeepax at opensource.cirrus.com>
> ---
>   include/sound/soc-component.h | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/include/sound/soc-component.h b/include/sound/soc-component.h
> index 766dc6f009c0b..5a764c3099d3e 100644
> --- a/include/sound/soc-component.h
> +++ b/include/sound/soc-component.h
> @@ -169,6 +169,15 @@ struct snd_soc_component_driver {
>   	unsigned int idle_bias_on:1;
>   	unsigned int suspend_bias_off:1;
>   	unsigned int use_pmdown_time:1; /* care pmdown_time at stop */
> +	/*
> +	 * Indicates that the component does not care about the endianness of
> +	 * PCM audio data and the core will ensure that both LE and BE variants
> +	 * of each used format are present. Typically this is because the
> +	 * component sits behind a bus that abstracts away the endian of the
> +	 * original data, ie. one for which the transmission endian is defined
> +	 * (I2S/SLIMbus/SoundWire), or the concept of endian doesn't exist (PDM,
> +	 * analogue).
> +	 */
>   	unsigned int endianness:1;
>   	unsigned int non_legacy_dai_naming:1;
>