RE: [alsa-devel] [PATCH] ASoC: atmel_ssc_dai: Track playback and capture CMR dividers separately.

[Peter Rosin <peda@axentia.se>]

Hi!

(and thank you for the pointer to the example with the ssc-dai in master mode)

> Hi Peter,
> 
> On 10/20/2014 09:45 PM, Peter Rosin wrote:
> >  From 1e5621d7b9887c648d1a66238dc82d715c1e2cad Mon Sep 17 00:00:00
> > 2001
> > From: Peter Rosin <peda@axentia.se>
> > Date: Mon, 20 Oct 2014 14:38:04 +0200
> > Subject: [PATCH] ASoC: atmel_ssc_dai: Track playback and capture CMR
> dividers
> >   separately.
> >
> > The CMR divider register is shared by playback and capture. The SSC
> > driver therefore tries to enforce rules so that the needed register
> > content do not conflict during simultaneous playback/capture. However,
> > the implementation also prevents changing the register content in a
> > half-duplex scenario, which is needed when changing sample rates.
> 
> I am not fully get what you mean here, do you mean:
>    - when playback, first playback 48kHz, and then playback 8Khz, the 8Khz still
> playback in 48kHz mode?
> 
> or other things?

I do not know exactly why the problem occurs, but it might be connected to
the library (proprietary) we are using. It apparently uses the OSS interface
and somehow it opens a stream and changes the playback sample-rate a
couple of time before it settles on something. I don't know why this is
done, and I have no control over it. The end result is that without this patch,
the ssc-dai driver returns -EBUSY when the library changes the playback
sample-rate (the driver returns -EBUSY because it thinks that the new
sample rate does not match a previously given capture sample-rate, but
that is of course bogus when no capture is going on at all).

> > Thus, keep track of the desired playback and capture clock dividers
> > separately, and allow changing rates without closing the stream.
> >
> > Signed-off-by: Peter Rosin <peda@axentia.se>
> > ---
> >   sound/soc/atmel/atmel_ssc_dai.c |   31 ++++++++++++++++++++++------
> ---
> >   sound/soc/atmel/atmel_ssc_dai.h |   10 ++++++----
> >   2 files changed, 28 insertions(+), 13 deletions(-)
> >
> > diff --git a/sound/soc/atmel/atmel_ssc_dai.c
> > b/sound/soc/atmel/atmel_ssc_dai.c index f403f39..fec14fb 100644
> > --- a/sound/soc/atmel/atmel_ssc_dai.c
> > +++ b/sound/soc/atmel/atmel_ssc_dai.c
> > @@ -277,7 +277,8 @@ static void atmel_ssc_shutdown(struct
> snd_pcm_substream *substream,
> >   		/* Reset the SSC */
> >   		ssc_writel(ssc_p->ssc->regs, CR, SSC_BIT(CR_SWRST));
> >   		/* Clear the SSC dividers */
> > -		ssc_p->cmr_div = ssc_p->tcmr_period = ssc_p->rcmr_period
> = 0;
> > +		ssc_p->tcmr_div = ssc_p->rcmr_div = 0;
> > +		ssc_p->tcmr_period = ssc_p->rcmr_period = 0;
> >   	}
> >   	spin_unlock_irq(&ssc_p->lock);
> >   }
> > @@ -304,17 +305,27 @@ static int atmel_ssc_set_dai_clkdiv(struct
> snd_soc_dai *cpu_dai,
> >   	struct atmel_ssc_info *ssc_p = &ssc_info[cpu_dai->id];
> >
> >   	switch (div_id) {
> > -	case ATMEL_SSC_CMR_DIV:
> > +	case ATMEL_SSC_TCMR_DIV:
> >   		/*
> >   		 * The same master clock divider is used for both
> >   		 * transmit and receive, so if a value has already
> > -		 * been set, it must match this value.
> > +		 * been set for the other direction, it must match
> > +		 * this value.
> >   		 */
> > -		if (ssc_p->cmr_div == 0)
> > -			ssc_p->cmr_div = div;
> > -		else
> > -			if (div != ssc_p->cmr_div)
> > -				return -EBUSY;
> > +		if (ssc_p->rcmr_div == 0)
> > +			ssc_p->tcmr_div = div;
> > +		else if (div != ssc_p->rcmr_div)
> > +			return -EBUSY;
> > +		break;
> > +
> > +	case ATMEL_SSC_RCMR_DIV:
> > +		/*
> > +		 * See ATMEL_SSC_TCMR_DIV.
> > +		 */
> > +		if (ssc_p->tcmr_div == 0)
> > +			ssc_p->rcmr_div = div;
> > +		else if (div != ssc_p->tcmr_div)
> > +			return -EBUSY;
> >   		break;
> >
> >   	case ATMEL_SSC_TCMR_PERIOD:
> > @@ -345,6 +356,7 @@ static int atmel_ssc_hw_params(struct
> snd_pcm_substream *substream,
> >   	struct atmel_pcm_dma_params *dma_params;
> >   	int dir, channels, bits;
> >   	u32 tfmr, rfmr, tcmr, rcmr;
> > +	u16 cmr;
> 
> should be u32.

Ok, I'll send an updated patch later.

> >   	int start_event;
> >   	int ret;
> >   	int fslen, fslen_ext;
> > @@ -626,7 +638,8 @@ static int atmel_ssc_hw_params(struct
> snd_pcm_substream *substream,
> >   	}
> >
> >   	/* set SSC clock mode register */
> > -	ssc_writel(ssc_p->ssc->regs, CMR, ssc_p->cmr_div);
> > +	cmr = ssc_p->tcmr_div ? ssc_p->tcmr_div : ssc_p->rcmr_div;
> > +	ssc_writel(ssc_p->ssc->regs, CMR, cmr);
> >
> >   	/* set receive clock mode and format */
> >   	ssc_writel(ssc_p->ssc->regs, RCMR, rcmr); diff --git
> > a/sound/soc/atmel/atmel_ssc_dai.h b/sound/soc/atmel/atmel_ssc_dai.h
> > index b1f08d5..a25df7a 100644
> > --- a/sound/soc/atmel/atmel_ssc_dai.h
> > +++ b/sound/soc/atmel/atmel_ssc_dai.h
> > @@ -39,9 +39,10 @@
> >   #define ATMEL_SYSCLK_MCK	0 /* SSC uses AT91 MCK as system
> clock */
> >
> >   /* SSC divider ids */
> > -#define ATMEL_SSC_CMR_DIV	0 /* MCK divider for BCLK */
> > -#define ATMEL_SSC_TCMR_PERIOD	1 /* BCLK divider for transmit FS */
> > -#define ATMEL_SSC_RCMR_PERIOD	2 /* BCLK divider for receive FS */
> > +#define ATMEL_SSC_TCMR_DIV	0 /* MCK divider for transmit BCLK */
> > +#define ATMEL_SSC_RCMR_DIV	1 /* MCK divider for receive BCLK */
> > +#define ATMEL_SSC_TCMR_PERIOD	2 /* BCLK divider for transmit
> FS */
> > +#define ATMEL_SSC_RCMR_PERIOD	3 /* BCLK divider for receive
> FS */
> >   /*
> >    * SSC direction masks
> >    */
> > @@ -110,7 +111,8 @@ struct atmel_ssc_info {
> >   	unsigned short dir_mask;	/* 0=unused, 1=playback, 2=capture
> */
> >   	unsigned short initialized;	/* true if SSC has been initialized */
> >   	unsigned short daifmt;
> > -	unsigned short cmr_div;
> > +	unsigned short tcmr_div;
> > +	unsigned short rcmr_div;
> >   	unsigned short tcmr_period;
> >   	unsigned short rcmr_period;
> >   	struct atmel_pcm_dma_params *dma_params[2];
> >
> 
> Best Regards,
> Bo Shen

Cheers,
Peter