linux-kernel - Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma

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Date:	Fri, 14 Sep 2012 10:12:25 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Tony Lindgren <tony@...mide.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Jarkko Nikula <jarkko.nikula@...mer.com>,
	alsa-devel@...a-project.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Janusz Krzysztofik <jkrzyszt@....icnet.pl>,
	Ricardo Neri <ricardo.neri@...com>
Subject: Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma_cyclic()

Hi,

On 09/13/2012 06:27 PM, Lars-Peter Clausen wrote:
> On 09/13/2012 03:37 PM, Peter Ujfalusi wrote:
>> The dmaengine_prep_dma_cyclic() function primarily used by audio for cyclic
>> transfer required by ALSA.
>> With this new parameter it is going to be possible to enable the
>> SNDRV_PCM_INFO_NO_PERIOD_WAKEUP mode on platforms where it is possible.
>> This patch only changes the public API first. Followup patch will change
>> the device_prep_dma_cyclic() callback parameters to pass this information
>> towards the dma drivers.
>>
> 
> Hi,
> 
> Hm... Do you think it would work as well if we implement this by setting the
> callback for the descriptor to NULL? If the callback is NULL there is
> nothing to at the end of a transfer/period and the dma engine driver may
> choose to disable interrupts. This would also benefit non cyclic transfers
> where the callback is NULL and we do not need add the new parameter to
> dmaengine_prep_dma_cyclic.

We could do that but dma drivers enable the interrupts within
dmaengine_prep_dma_cyclic() call, and we fill up the callback for
dmaengine_submit() dmaengine API call.
We need to tell the dma drivers in dmaengine_prep_dma_cyclic() to suppress the
interrupts.

Note: First I was trying this to be done in hw_params() time via the
dmaengine_slave_config() call, but substream->runtime->no_period_wakeup is not
configured in there. It is set for _prepare() and _trigger().

As Vinod and Russell suggested I will modify the dmaengine_prep_dma_cyclic()
API to pass flags as well instead of the no_wakeup parameter.

> 
> - Lars
> 
>> ---
>>  include/linux/dmaengine.h     | 3 ++-
>>  sound/soc/soc-dmaengine-pcm.c | 3 ++-
>>  2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>> index 9c02a45..990444b 100644
>> --- a/include/linux/dmaengine.h
>> +++ b/include/linux/dmaengine.h
>> @@ -653,7 +653,8 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_rio_sg(
>>  
>>  static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_cyclic(
>>  		struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
>> -		size_t period_len, enum dma_transfer_direction dir)
>> +		size_t period_len, enum dma_transfer_direction dir,
>> +		bool no_wakeup)
>>  {
>>  	return chan->device->device_prep_dma_cyclic(chan, buf_addr, buf_len,
>>  						period_len, dir, NULL);
>> diff --git a/sound/soc/soc-dmaengine-pcm.c b/sound/soc/soc-dmaengine-pcm.c
>> index 5df529e..6b70adb 100644
>> --- a/sound/soc/soc-dmaengine-pcm.c
>> +++ b/sound/soc/soc-dmaengine-pcm.c
>> @@ -147,7 +147,8 @@ static int dmaengine_pcm_prepare_and_submit(struct snd_pcm_substream *substream)
>>  	desc = dmaengine_prep_dma_cyclic(chan,
>>  		substream->runtime->dma_addr,
>>  		snd_pcm_lib_buffer_bytes(substream),
>> -		snd_pcm_lib_period_bytes(substream), direction);
>> +		snd_pcm_lib_period_bytes(substream), direction,
>> +		substream->runtime->no_period_wakeup);
>>  
>>  	if (!desc)
>>  		return -ENOMEM;
> 


-- 
Péter
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