linux-kernel - Re: [PATCH 12/18] ASoC: codecs: mt6357: add MT6357 codec

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Date: Fri, 15 Mar 2024 18:09:36 +0000
From: Mark Brown <broonie@...nel.org>
To: Alexandre Mergnat <amergnat@...libre.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Lee Jones <lee@...nel.org>, Flora Fu <flora.fu@...iatek.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, linux-sound@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	Nicolas Belin <nbelin@...libre.com>
Subject: Re: [PATCH 12/18] ASoC: codecs: mt6357: add MT6357 codec

On Fri, Mar 15, 2024 at 06:36:19PM +0100, Alexandre Mergnat wrote:
> On 15/03/2024 16:15, Mark Brown wrote:
> > On Fri, Mar 15, 2024 at 04:05:21PM +0100, Alexandre Mergnat wrote:

> > > > In the register.  You only need to reset the gain to -40dB at the start
> > > > of the ramp.

> > > Sorry but I don't understand your logic, I'm not able to implement it...
> > > If I'm at -10dB and doing a ramp to reach -40dB, next time I will read the
> > > register the value will be -40dB.

> > After we've done the ramp and turned the amplifier off we can just
> > restore the desired value?  The hardware is not going to care what the
> > volume is while it's not enabled.

> If you do that, HP will be enabled at the saved gain, and after that you
> will do the ramp. To avoid pop, the driver should be rewrite to:

So reset the volume to -40dB prior to turning the amplifier on...

>   Read gain in the reg and save it locally
>   Set -40dB in the reg
>   Enable HP
>   Do ramp

..as you yourself suggest?

> > > AFAII from the comment in the code, it's done to avoid the "pop noises".

> > Yes, that's the usual reason to ramp gains.  Though if you've just
> > copied the code without checking that it's needed it's possible that
> > this is something that's been fixed in current hardware.

> I did the test at 24dB with and without the "pop filter". Isn't big but I
> ear the pop at the start of the record without the "pop filter".

OK, it probably is still doing something then.

> To be clear, the algo/behavior of this code is an implementation based on
> the 6k+ lines downstream code for this specific audio codec. But the
> shape/style is based on upstreamed drivers like mt6358.c.

The Mediatek code has a bunch of issues, I wouldn't read too much into
something being present in the code.

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