linux-kernel - Re: [PATCH 1/1] ASoC: sunxi: sun4i-i2s: fix LRCLK polarity in i2s mode

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Message-ID: <20240715-rigorous-bipedal-sloth-c8df1b@houat>
Date: Mon, 15 Jul 2024 16:29:52 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Matteo Martelli <matteomartelli3@...il.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, Chen-Yu Tsai <wens@...e.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Marcus Cooper <codekipper@...il.com>, Clément Péron <peron.clem@...il.com>, 
	linux-sound@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ASoC: sunxi: sun4i-i2s: fix LRCLK polarity in i2s
 mode

On Tue, Jul 02, 2024 at 05:17:15PM GMT, Matteo Martelli wrote:
> Maxime Ripard wrote:
> > On Fri, Jun 07, 2024 at 10:04:43AM GMT, Matteo Martelli wrote:
> > > Maxime Ripard wrote:
> > > > > -	/*
> > > > > -	 * DAI clock polarity
> > > > > -	 *
> > > > > -	 * The setup for LRCK contradicts the datasheet, but under a
> > > > > -	 * scope it's clear that the LRCK polarity is reversed
> > > > > -	 * compared to the expected polarity on the bus.
> > > > > -	 */
> > > > 
> > > > I think we should keep that comment somewhere.
> > > 
> > > I think that keeping that comment would be very misleading since the LRCLK
> > > setup would not contradict the datasheet anymore [1][2].
> > >
> > > Also, do you recall any details about the mentioned scope test setup? Was i2s
> > > mode tested in that occasion? It would help clarify the situation.
> > 
> > I can't remember if I tested i2s, I think I did though. But most of the
> > work was done on either TDM or DSP modes, and I remember very clearly
> > that the LRCK polarity was inverted compared to what Allwinner documents.
> > 
> > So the doc was, at best, misleading for these formats and we should keep
> > the comments.
> 
> Thanks for the reply Maxime, would you be able to point out the Allwinner
> document part that is (or was) misleading? The current datasheets (see links
> [1][2]) look correct, the current driver setup for TDM and DSP modes respects
> those datasheets and it's not "reversed compared to the expected polarity on
> the bus" as the comment states. 

I clearly remember having to debug something there, but I don't remember
much more, sorry.

I guess if you have tested on the H3 I2S, TDM and DSP and it all works
as expected with your changes, go ahead and ignore my comment then.

> Also I didn't find any related errata in their changelog. 

Yeah... Allwinner doesn't do errata.

> Could it be possible that during those mentioned tests you
> were still referring to the datasheets of other SoCs like A10 for
> instance? Or maybe that the misleading information was in another
> document rather than the main datasheets? If that's the case, would
> you still think that the comment should be kept as it is?

Possibly, or an older version of the datasheet, I really can't remember.

Maxime

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