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

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Date:   Mon, 18 Dec 2017 09:31:22 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     chen liu <chen.liu.opensource@...il.com>
CC:     <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 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:
> When the MCLK clock frequency cannot meet the SYSCLK clock
> frequency of the wm8960 codec,we must use the PLL divider to
> generate the clock frequency.
> 
> For what you are talking about setting the SYSCLK clock frequency
> automatically and manually,the difference is that one uses the PLL
> divider to generate the SYSCLK clock frequency and the other one
> provides the SYSCLK clock frequency directly through the MCLK.
> 
> Although the driver already supports setting the SYSCLK_DIV register,
> it can only be set to 1,thus causing the codec to not support multiple
> MCLK clock frequency.(For more information, please see the wm8960
> codec manual)
> 
> The important purpose of this patch is to support multiple MCLK
> clock frequency.

Sorry I think I am not following something here, could you be a
bit more specific, especially about why the automatic approach
doesn't meet your needs.

As far as I can see this will let you set the SYSCLKDIV using the
manual method and it can be easily set to either 1 or 2:

static int wm8960_set_dai_clkdiv(struct snd_soc_dai *codec_dai,
...
	switch (div_id) {
		case WM8960_SYSCLKDIV:
			reg = snd_soc_read(codec, WM8960_CLOCK1) & 0x1f9;
		snd_soc_write(codec, WM8960_CLOCK1, reg | div);
		break;
...

And as for the automatic method:

static int wm8960_configure_pll(struct snd_soc_codec *codec, int freq_in,
...
	for (i = 0; i < ARRAY_SIZE(sysclk_divs); ++i) {
		if (sysclk_divs[i] == -1) continue;
...

This will iterate through all the sysclk_dividers and pick one
that is appropriate either 1 or 2. So in what way does the
automatic method not support a SYSCLK_DIV of 2?

Thanks,
Charles