[alsa-devel] [PATCH] ASoC: davinci-mcasp: Add clocking option

[Peter Ujfalusi]

Please do CC the maintainers when sending patches.

On 07/26/16 15:05, Stefan Müller-Klieser wrote:
> The AHCLKX clock output of the McASP can be used as audio MCLK, even
> if the McASP runs in slave mode. Add a DT binding to make this option
> available in a simple-card setup.

In other words: McASP is clock master, but we want to have the HCLK to be
coming from internal AUXCLK and not from the AHCLKX pin, right?
There might be also cases when McASP is slave _and_ we want to configure the
HCLK from the AHCLKX ping. Adding new flag for this is not a good idea IMHO.

This is simply a workaround for the current simple card and might break if
something is changing in there..

I'm aware that this is a problematic issue. We can not have clock id support
in the simple-card and I don't think it is a good idea to hack around this in
the McASP driver.
I don't see any other way right now then moving the McASP driver to CCF, or at
first probably add CCF support to configure the clock routes while still
keeping the ASoC way of configuring the clocks.

> Signed-off-by: Stefan Müller-Klieser <s.mueller-klieser at phytec.de>
> ---
>  Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt | 4 ++++
>  include/linux/platform_data/davinci_asp.h                       | 5 +++++
>  sound/soc/davinci/davinci-mcasp.c                               | 8 ++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt b/Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt
> index 46bc982..96d6244 100644
> --- a/Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt
> +++ b/Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt
> @@ -39,6 +39,10 @@ Optional properties:
>    		 please refer to pinctrl-bindings.txt
>  - fck_parent : Should contain a valid clock name which will be used as parent
>  	       for the McASP fck
> +- ahclkx-en: In case the MCASP runs in slave mode, e.g. i2s SCK and WS slave,
> +             we can still provide the MCLK to a codec PLL using the AHCLKX
> +             transmit clock output. This setup can be activated by using this
> +             property. Clock master mode remains unaffected.

_if_ we hack this around in the driver I would rather have something like:
hclk-source: Source of HCLK internal clock when McASP is clock master.
With a new DT binding header file with defines:

/* Source of High-frequency transmit/receive clock */
#define MCASP_CLK_HCLK_AHCLK		0 /* AHCLKX/R */
#define MCASP_CLK_HCLK_AUXCLK		1 /* Internal functional clock */

Basically my old patches for McASP clock selection but w/o the improving the
simple card.
The only change would be that we ignore the set_sysclk's clk_id parameter and
use the private clk_id we got via DT when the dir is SND_SOC_CLOCK_IN.
Oh, and set the PDIR also when AUXCLK is selected for HCLK.
In the DT you would have for your setup:

hclk-source = MCASP_CLK_HCLK_AUXCLK;

Or something like that.

But I think in this way we can work around the simple-card posed limitation a
bit better, but it is still a questionable workaround.

I have attached my local patches for reference.

>  
>  Example:
>  
> diff --git a/include/linux/platform_data/davinci_asp.h b/include/linux/platform_data/davinci_asp.h
> index 85ad68f..c878836 100644
> --- a/include/linux/platform_data/davinci_asp.h
> +++ b/include/linux/platform_data/davinci_asp.h
> @@ -44,6 +44,11 @@ struct davinci_mcasp_pdata {
>  	int clk_input_pin;
>  
>  	/*
> +	 * Activate AHCLKX clock output in slave mode.
> +	 */
> +	bool ahclkx_en;
> +
> +	/*
>  	 * This flag works when both clock and FS are outputs for the cpu
>  	 * and makes clock more accurate (FS is not symmetrical and the
>  	 * clock is very fast.
> diff --git a/sound/soc/davinci/davinci-mcasp.c b/sound/soc/davinci/davinci-mcasp.c
> index 237dc67..aba888e 100644
> --- a/sound/soc/davinci/davinci-mcasp.c
> +++ b/sound/soc/davinci/davinci-mcasp.c
> @@ -94,6 +94,7 @@ struct davinci_mcasp {
>  
>  	int	sysclk_freq;
>  	bool	bclk_master;
> +	bool    ahclkx_en;
>  
>  	/* McASP FIFO related */
>  	u8	txnumevt;
> @@ -605,6 +606,10 @@ static int davinci_mcasp_set_sysclk(struct snd_soc_dai *dai, int clk_id,
>  		mcasp_set_bits(mcasp, DAVINCI_MCASP_AHCLKXCTL_REG, AHCLKXE);
>  		mcasp_set_bits(mcasp, DAVINCI_MCASP_AHCLKRCTL_REG, AHCLKRE);
>  		mcasp_set_bits(mcasp, DAVINCI_MCASP_PDIR_REG, AHCLKX);
> +	} else if (mcasp->ahclkx_en) {
> +		mcasp_clr_bits(mcasp, DAVINCI_MCASP_AHCLKRCTL_REG, AHCLKRE);

It is safe to set this bit as well.

> +		mcasp_set_bits(mcasp, DAVINCI_MCASP_AHCLKXCTL_REG, AHCLKXE);
> +		mcasp_set_bits(mcasp, DAVINCI_MCASP_PDIR_REG, AHCLKX);
>  	} else {
>  		mcasp_clr_bits(mcasp, DAVINCI_MCASP_AHCLKXCTL_REG, AHCLKXE);
>  		mcasp_clr_bits(mcasp, DAVINCI_MCASP_AHCLKRCTL_REG, AHCLKRE);
> @@ -1610,6 +1615,8 @@ static struct davinci_mcasp_pdata *davinci_mcasp_set_pdata_from_of(
>  	if (ret >= 0)
>  		pdata->op_mode = val;
>  
> +	pdata->ahclkx_en = of_property_read_bool(np, "ahclkx-en");
> +
>  	ret = of_property_read_u32(np, "tdm-slots", &val);
>  	if (ret >= 0) {
>  		if (val < 2 || val > 32) {
> @@ -1851,6 +1858,7 @@ static int davinci_mcasp_probe(struct platform_device *pdev)
>  	mcasp->version = pdata->version;
>  	mcasp->txnumevt = pdata->txnumevt;
>  	mcasp->rxnumevt = pdata->rxnumevt;
> +	mcasp->ahclkx_en = pdata->ahclkx_en;
>  
>  	mcasp->dev = &pdev->dev;
>  
> 


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