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

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Message-ID: <1j1q7fpv1n.fsf@starbuckisacylon.baylibre.com>
Date: Mon, 08 Apr 2024 20:15:54 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Dmitry Rokosov <ddrokosov@...utedevices.com>
Cc: neil.armstrong@...aro.org, lgirdwood@...il.com, jbrunet@...libre.com,
 broonie@...nel.org, conor+dt@...nel.org, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, perex@...ex.cz, tiwai@...e.com,
 khilman@...libre.com, martin.blumenstingl@...glemail.com,
 kernel@...utedevices.com, rockosov@...il.com,
 linux-amlogic@...ts.infradead.org, alsa-devel@...a-project.org,
 linux-sound@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 2/2] ASoC: meson: implement link-name optional
 property in meson card utils


On Mon 08 Apr 2024 at 19:49, Dmitry Rokosov <ddrokosov@...utedevices.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 previous naming approach using auto-generated fe or be strings
> continues to be utilized as a fallback.
>
> Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.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