linux-kernel - Re: [PATCH] ASoC: es8316: limit headphone mixer volume

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Date:   Mon, 26 Aug 2019 10:53:15 +0800
From:   Daniel Drake <drake@...lessm.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Katsuhiro Suzuki <katsuhiro@...suster.net>,
        Mark Brown <broonie@...nel.org>,
        David Yang <yangxiaohua@...rest-semi.com>,
        alsa-devel@...a-project.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: es8316: limit headphone mixer volume

On Mon, Aug 26, 2019 at 1:38 AM Hans de Goede <hdegoede@...hat.com> wrote:
> On 24-08-19 23:04, Katsuhiro Suzuki wrote:
> > This patch limits Headphone mixer volume to 4 from 7.
> > Because output sound suddenly becomes very loudly with many noise if
> > set volume over 4.

That sounds like something that should be limited in UCM.

> Higher then 4 not working matches my experience, see this comment from
> the UCM file: alsa-lib/src/conf/ucm/codecs/es8316/EnableSeq.conf :
>
> # Set HP mixer vol to -6 dB (4/7) louder does not work
> cset "name='Headphone Mixer Volume' 4"

What does "does not work" mean more precisely?

I checked the spec, there is indeed something wrong in the kernel driver here.
The db scale is not a simple scale as the kernel source suggests.

Instead it is:
0000 – -12dB
0001 – -10.5dB
0010 – -9dB
0011 – -7.5dB
0100 – -6dB
1000 – -4.5dB
1001 – -3dB
1010 – -1.5dB
1011 – 0dB

So perhaps we can fix the kernel to follow this table and then use UCM
to limit the volume if its too high on a given platform?

Thanks
Daniel