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Date:   Fri, 07 Jul 2023 15:47:47 +0200
Message-ID: <87v8evkf3w.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Mark Brown <broonie@kernel.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Johan Hovold <johan@kernel.org>, perex@perex.cz,
        tiwai@suse.com, lgirdwood@gmail.com, ckeepax@opensource.cirrus.com,
        kuninori.morimoto.gx@renesas.com, linux-kernel@vger.kernel.org,
        pierre-louis.bossart@linux.intel.com, alsa-devel@alsa-project.org
Subject: Re: [PATCH] ASoC: codecs: wcd938x: fix dB range for HPHL and HPHR
In-Reply-To: <f1041542-bd97-41d9-96b9-c6e5fef6b096@sirena.org.uk>
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        <efaf5960-bcc5-6d52-5552-e1505a13b635@linaro.org>
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        <3450ef1e-cb20-4242-b482-41d3d34c4564@sirena.org.uk>
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        <f1041542-bd97-41d9-96b9-c6e5fef6b096@sirena.org.uk>
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On Fri, 07 Jul 2023 15:35:29 +0200,
Mark Brown wrote:
> 
> On Fri, Jul 07, 2023 at 03:30:48PM +0200, Takashi Iwai wrote:
> > Mark Brown wrote:
> 
> > > It's moderately common - typically in these cases the control is
> > > described in the datasheet as an attenuation control rather than a gain,
> > > and this usually corresponds to the physical implementation being only
> > > able to make signals smaller relative to the reference.
> 
> > Yeah, I see the use case.  The problem is, however, that we're using
> > the very same dB info for both gain and attenuation.  That means,
> > application has no idea how to interpret those dB values -- to be
> > added or to be subtracted.
> 
> > We should have defined a new TLV type for attenuation to
> > differentiate, and define the TLV macro to give proper min/max.
> 
> The ASoC generic control stuff supports inverting the value prior to
> presentation to userspace so it's masked there (instead of writing the
> number userspace sees to the register we subtract the number from the
> maximum value and write that to the register), pulling that up further
> to the ALSA core might be nice I guess?

I believe yes.  Though, I'm still not sure how we can improve the
mismatch of dB min/max.  The dB values of those inverted controls
reflect the result of subtraction, no?


Takashi