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

21 Oct 2014

Hi Peter,
On 10/21/2014 03:55 PM, Peter Rosin wrote:
...
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).
If this issue is caused by your proprietary library, please fix in the 
library.
I don't know how this code can fix your issue and also there is no 
improvement to the code and it absolutely increase work (choose which 
clock to configure: tcmr or rcmr) for the SSC work in master. And also 
this patch may confuse the end user, let them thinking the clock for 
tcmr and rcmr can configure seperately.
So, I think keep the code as is (without this patch applied), what's 
your opinion?
...
...
...
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
Best Regards,
Bo Shen

    