[alsa-devel] [RFC PATCH] Add combined clock support to Atmel SoC audio

[Ryan Mallon]

On 11/24/2010 12:29 PM, Mark Brown wrote:
> On Wed, Nov 24, 2010 at 11:05:11AM +1300, Ryan Mallon wrote:
> 
>> This patch is posted as RFC since the approach is incomplete and a bit
>> hackish. I am mostly interested in knowing if this is a sensible
>> approach, and could be cleaned up for mainline inclusion, or if there is
>> a better way to do this.
> 
> This doesn't look obviously hideous.

Thanks :-)

> It should set the symmetric_rates flag when going into combined clocks
> mode.  A few other comments:
> 
>> +			if (atomic_dec_and_test(&ssc_p->substreams_running))
>> +				ssc_writel(ssc_p->ssc->regs, CR,
>> +					   dma_params->mask->ssc_disable);

Okay.

> It'd seem clearer to use a regular lock here; probably safer also as you
> could get a race between the test and the write which tries to revert
> the change - ie a:
> 
> 	dec_and_test
> 			inc
> 			read
> 			write
> 	write
>
> type pattern.

Okay, regular spin_lock should be okay right?

>> +	if (ssc_p->combined_clock == ATMEL_SSC_CLOCK_RX_ON_TX) {
> 
> How about just calling these defines ATMEL_SSC_CLOCK_TX or _RX?  You're
> identifying the clock line to use for both cases, it's probably clearer
> to say "use the RX lines" or "use the TX" lines than say "do one on the
> other" if you see what I mean.

Okay, will change.

> 
>> +		/* RX clock is sourced from TK pin */
>> +		rcmr &= ~SSC_BF(RCMR_CKS, 0x7);
>> +		rcmr |=  SSC_BF(RCMR_CKS, SSC_CKS_CLOCK);
>
> Is this done by the driver normally, or is it done by the machine
> normally?  If it's normally done by the machine perhaps it should be
> moved into the driver in all cases.

Essentially this code is overriding the settings in the hw_params switch
statement for the combined clocks case. This will need to be overridden
each time hw_params is called. Doing it here seems logical since
atmel_ssc_dai:hw_params does the original setting. It keeps the machine
drivers simpler too.

>> +		if (dir == 1) {
>> +			/*
>> +			 * Set the TX clock period to the RX clock period
>> +			 * FIXME - Is this okay if we are already doing TX?
>> +			 */
>> +			tcmr &= 0x00ffffff;
>> +			tcmr |= rcmr & 0xff000000;
> 
> Should probably enforce a constraint to stop users doing something that
> forces the change?

Okay. Could you point me at an example for this please.

Thanks,
~Ryan

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