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

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Date: Tue, 02 Jul 2024 17:17:15 +0200
From: Matteo Martelli <matteomartelli3@...il.com>
To: Maxime Ripard <mripard@...nel.org>
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

Maxime Ripard wrote:
> Hi,
> 
> 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.
> 
> Maxime

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

[1]: https://linux-sunxi.org/images/4/4b/Allwinner_H3_Datasheet_V1.2.pdf
section 8.6.7.2
[2]: https://linux-sunxi.org/images/4/46/Allwinner_H6_V200_User_Manual_V1.1.pdf
section 7.2.5.2

Thanks,
Matteo