linux-kernel - Re: [PATCH v2 01/12] ALSA: doc: Clarify IEC958 controls iface

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Date:   Tue, 25 May 2021 17:58:29 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Mark Brown <broonie@...nel.org>,
        dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Liam Girdwood <lgirdwood@...il.com>,
        Takashi Iwai <tiwai@...e.com>, devicetree@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Dom Cobley <dom@...pberrypi.com>, linux-doc@...r.kernel.org,
        Eric Anholt <eric@...olt.net>,
        Nicolas Saenz Julienne <nsaenzjulienne@...nel.org>,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        Maxime Ripard <mripard@...nel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org,
        Daniel Vetter <daniel@...ll.ch>,
        linux-rpi-kernel@...ts.infradead.org,
        Jonathan Corbet <corbet@....net>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v2 01/12] ALSA: doc: Clarify IEC958 controls iface

On Tue, 25 May 2021 15:23:43 +0200,
Maxime Ripard wrote:
> 
> The doc currently mentions that the IEC958 Playback Default should be
> exposed on the PCM iface, and the Playback Mask on the mixer iface.
> 
> It's a bit confusing to advise to have two related controls on two
> separate ifaces, and it looks like the drivers that currently expose
> those controls use any combination of the mixer and PCM ifaces.
> 
> Let's try to clarify the situation a bit, and encourage to at least have
> the controls on the same iface.
> 
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Reviewed-by: Takashi Iwai <tiwai@...e.de>


thanks,

Takashi


> ---
>  .../sound/kernel-api/writing-an-alsa-driver.rst     | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
> index e6365836fa8b..01d59b8aea92 100644
> --- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
> +++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
> @@ -3508,14 +3508,15 @@ field must be set, though).
>  
>  “IEC958 Playback Con Mask” is used to return the bit-mask for the IEC958
>  status bits of consumer mode. Similarly, “IEC958 Playback Pro Mask”
> -returns the bitmask for professional mode. They are read-only controls,
> -and are defined as MIXER controls (iface =
> -``SNDRV_CTL_ELEM_IFACE_MIXER``).
> +returns the bitmask for professional mode. They are read-only controls.
>  
>  Meanwhile, “IEC958 Playback Default” control is defined for getting and
> -setting the current default IEC958 bits. Note that this one is usually
> -defined as a PCM control (iface = ``SNDRV_CTL_ELEM_IFACE_PCM``),
> -although in some places it's defined as a MIXER control.
> +setting the current default IEC958 bits.
> +
> +Due to historical reasons, both variants of the Playback Mask and the
> +Playback Default controls can be implemented on either a
> +``SNDRV_CTL_ELEM_IFACE_PCM`` or a ``SNDRV_CTL_ELEM_IFACE_MIXER`` iface.
> +Drivers should expose the mask and default on the same iface though.
>  
>  In addition, you can define the control switches to enable/disable or to
>  set the raw bit mode. The implementation will depend on the chip, but
> -- 
> 2.31.1
>