linux-kernel - Re: [PATCH v2 2/2] ASoC: codec: wm8960: Relax bit clock computation

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Message-ID: <20170321125207.GX6986@localhost.localdomain>
Date:   Tue, 21 Mar 2017 12:52:07 +0000
From:   Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:     Daniel Baluta <daniel.baluta@....com>
CC:     <lgirdwood@...il.com>, <broonie@...nel.org>, <tiwai@...e.com>,
        <patches@...nsource.wolfsonmicro.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <shengjiu.wang@...escale.com>, <mihai.serban@....com>,
        <viorel.suman@....com>
Subject: Re: [PATCH v2 2/2] ASoC: codec: wm8960: Relax bit clock computation

On Tue, Mar 21, 2017 at 12:09:36PM +0200, Daniel Baluta wrote:
> WM8960 derives bit clock from sysclock using BCLKDIV[3:0] of R8
> clocking register (See WM8960 datasheet, page 71).
> 
> There are use cases, like this:
> aplay -Dhw:0,0 -r 48000 -c 1 -f S20_3LE -t raw audio48k20b_3LE1c.pcm
> 
> where no BCLKDIV applied to sysclock can give us the exact requested
> bitclk, so driver fails to configure clocking and aplay fails to run.
> 
> Fix this by relaxing bitclk computation, so that when no exact value
> can be derived from sysclk pick the closest value greater than
> expected bitclk.
> 
> Suggested-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
> Signed-off-by: Daniel Baluta <daniel.baluta@....com>
> ---
> Changes since v1:
> 	* use a marker to check if a match is found
> 	* didn't removed PLL as Charles suggested because there is
> 	a special PLL mode which explictly uses PLL. We could start
> 	a discussion on not using PLL when deriving bitclk, but this
> 	is to be done in another patch.
> 

Could you elaborate on this a little more am I not sure I follow
100%? There is a mode which explictly requires the PLL to be used
(WM8960_SYSCLK_PLL) but in that case your wm8960_configure_sysclk
code will not be called so I don't see what is causing that to have
an effect on this patch?

Thanks,
Charles