linux-kernel - Re: [PATCH v2] ASOC: wm8960: Add multiple MCLK frequency support

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Date:   Thu, 21 Dec 2017 16:48:10 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     chen liu <chen.liu.opensource@...il.com>
CC:     Liam Girdwood <lgirdwood@...il.com>, <broonie@...nel.org>,
        <perex@...ex.cz>, <tiwai@...e.com>, <shengjiu.wang@...escale.com>,
        <linux-kernel@...r.kernel.org>, <daniel.baluta@....com>,
        <patches@...nsource.wolfsonmicro.com>,
        <alsa-devel@...a-project.org>
Subject: Re: [PATCH v2] ASOC: wm8960: Add multiple MCLK frequency support

On Tue, Dec 19, 2017 at 02:19:48PM +0800, chen liu wrote:
> 2017-12-18 19:55 GMT+08:00 Charles Keepax <ckeepax@...nsource.cirrus.com>:
> > On Mon, Dec 18, 2017 at 07:32:41PM +0800, chen liu wrote:
> > > 2017-12-18 17:31 GMT+08:00 Charles Keepax <ckeepax@...nsource.cirrus.com
> > > > On Fri, Dec 15, 2017 at 09:07:15PM +0800, chen liu wrote:
> > > > > 2017-12-15 0:19 GMT+08:00 Charles Keepax <
> > ckeepax@...nsource.cirrus.com
> > > > > > On Wed, Dec 13, 2017 at 08:37:30PM +0800, Chen.Liu wrote:
>         // Then this branch will be executed.
>         //  If the sample rate is 44100HZ, the value of freq_out will be
> 11.2896MHZ
>         freq_out = wm8960_configure_pll(codec, freq_in, &i, &j, &k);
>         if (freq_out < 0) {
>                 dev_err(codec->dev, "failed to configure clock via PLL\n");
>                 return freq_out;
>         }
>        // The 'wm8960_set_pll' function will be executed,this function is
> very important.
>        // But now, the freq_in is 24MHZ and the freq_out is 11.2896MHZ.
>         wm8960_set_pll(codec, freq_in, freq_out);
> ...
> 
> Because the 'wm8960_configure_pll' function has been pre-scaled by 2 for
> freq_out,
> but the value of freq_out is not multiplied by 2 in the 'pll_factors'
> function, it prints the
> "WM8960 PLL: Unsupported N =" error message.

Ah ok so I hadn't realised you were using the SYSCLK_AUTO stuff
and finding an issue with it. Thank you very much for the
explanation.

One thing I don't understand though is it looks like the freq_out
returned from wm8960_configure_pll should already be taking the
SYSCLK_DIV into account:

for (j = 0; j < ARRAY_SIZE(dac_divs); ++j) {
	sysclk = lrclk * dac_divs[j];
	freq_out = sysclk * sysclk_divs[i];

So if lrclk=44100, j=0, i=2 which I believe is the case in
question we should get:

sysclk = 44100 * 256 = 11.2896MHz
freq_out = 11.2896MHz * 2 = 22.5792MHz

So when wm8960_configure_pll returns i=2 then it should also be
setting freq_out as 22.5792MHz. So you final call there to
wm8960_set_pll should be:

wm8960_set_pll(codec, 24MHz, 22.5792MHz);

Can you see why that isn't happening?

Thanks,
Charles