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SubjectRe: [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;
>


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