linux-kernel - Re: [PATCH] ASoC: rockchip: i2s: Support mono capture

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Message-ID: <20180109163943.GC11471@sirena.org.uk>
Date:   Tue, 9 Jan 2018 16:39:43 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Heiko Stuebner <heiko@...ech.de>, alsa-devel@...a-project.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Dylan Reid <dgreid@...omium.org>
Subject: Re: [PATCH] ASoC: rockchip: i2s: Support mono capture

On Mon, Jan 08, 2018 at 04:01:15PM -0800, Matthias Kaehlcke wrote:

> Due to different issues in our audio recording path I couldn't test
> this properly, and only looked at the .wav data in audacity, which
> appeared to look ok. After putting some of the missing pieces
> together and I noticed that mono capture doesn't work as intended,
> the recorded audio is slowed down. I think this is because the I2S
> controller keeps generating a two-channel stream, however the sound
> system interprets it as a monophonic stream because of the channel
> configuration.

That seems odd - I'd expect underruns somewhere?

> Not sure if there is a clean solution for this if we can't tell the
> hardware to generate a single-channel stream. Any suggestions or do
> we have to revert the patch?

It sounds like a very standard problem with I2S devices, it's a
fundamentally stereo format after all.  If you can't get it to discard
the second channel there's probably not much doing.

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