[PATCH v1 2/2] ASoC: meson: implement link-name optional property in meson card utils

[Jerome Brunet]

On Mon 08 Apr 2024 at 21:40, Dmitry Rokosov <ddrokosov at salutedevices.com> wrote:

> On Mon, Apr 08, 2024 at 08:15:54PM +0200, Jerome Brunet wrote:
>> 
>> On Mon 08 Apr 2024 at 19:49, Dmitry Rokosov <ddrokosov at salutedevices.com> wrote:
>> 
>> > The 'link-name' property presents an optional DT feature that empowers
>> > users to customize the name associated with the DAI link and PCM stream.
>> > This functionality reflects the approach often employed in Qualcomm
>> > audio cards, providing enhanced flexibility in DAI naming conventions
>> > for improved system integration and userspace experience.
>> >
>> > It allows userspace program to easy determine PCM stream purpose, e.g.:
>> >     ~ # cat /proc/asound/pcm
>> >     00-00: speaker (*) :  : playback 1
>> >     00-01: mics (*) :  : capture 1
>> >     00-02: loopback (*) :  : capture 1
>> 
>> The example above is exactly what you should not do with link names, at
>> least with the amlogic audio system.
>> 
>> Userspace pcm, otherwise known as DPCM frontend, are merely that:
>> frontends. What they do is entirely defined by the routing defined by
>> the userspace (amixer and friends)
>> 
>> So naming the interface in DT (the FW describing the HW) after what the
>> the userspace SW could possibly set later on is wrong.
>> 
>> Bottom line: I have mixed feeling about this change. It could allow all
>> sort of bad names to be set.
>> 
>> The only way it could make sense HW wise is if the only allowed names
>> where (fr|to)ddr_[abcd], which could help maps the interface and the
>> kcontrol.
>> 
>> Such restriction should be documented in the binding doc.
>> 
>
> The link-name is an optional parameter. Yes, you are right, it can be
> routed in a way that it no longer functions as a speaker in most cases.
> However, if you plan to use your board's dt for common purposes, you
> should not change the common names for DAI links. But if you know that
> you have a static setup for speakers, microphones, loopback, or other
> references (you 100% know it, because you are HW developer of this
> board), why not help the user understand the PCM device assignment in
> the easiest way?
>
> Ultimately, it is the responsibility of the DT board developer to define
> specific DAIs and name them based on their own knowledge about HW and
> understanding of the board's usage purposes.

Speaker and mics are NOT statically tied to a frontend. They are tied to a
codec (... possibly). The routing from the frontend to the backend is
dynamic, even while streaming.

So defining FW names based on usage in wrong.
As Mark pointed out as well, DT is not the place for this.

>
>> >
>> > The previous naming approach using auto-generated fe or be strings
>> > continues to be utilized as a fallback.
>> >
>> > Signed-off-by: Dmitry Rokosov <ddrokosov at salutedevices.com>
>> > ---
>> >  sound/soc/meson/meson-card-utils.c | 12 ++++++++----
>> >  1 file changed, 8 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/sound/soc/meson/meson-card-utils.c b/sound/soc/meson/meson-card-utils.c
>> > index ed6c7e2f609c..7bae72905a9b 100644
>> > --- a/sound/soc/meson/meson-card-utils.c
>> > +++ b/sound/soc/meson/meson-card-utils.c
>> > @@ -94,10 +94,14 @@ static int meson_card_set_link_name(struct snd_soc_card *card,
>> >  				    struct device_node *node,
>> >  				    const char *prefix)
>> >  {
>> > -	char *name = devm_kasprintf(card->dev, GFP_KERNEL, "%s.%s",
>> > -				    prefix, node->full_name);
>> > -	if (!name)
>> > -		return -ENOMEM;
>> > +	const char *name;
>> > +
>> > +	if (of_property_read_string(node, "link-name", &name)) {
>> > +		name = devm_kasprintf(card->dev, GFP_KERNEL, "%s.%s",
>> > +				      prefix, node->full_name);
>> > +		if (!name)
>> > +			return -ENOMEM;
>> > +	}
>> >  
>> >  	link->name = name;
>> >  	link->stream_name = name;
>> 
>> 
>> -- 
>> Jerome


-- 
Jerome