[alsa-devel] [PATCH v2 1/2] ASoC: dmaengine-pcm: Add support for querying DMA capabilities

[Vinod Koul]

On Tue, Oct 08, 2013 at 06:13:56PM +0200, Lars-Peter Clausen wrote:
> On 10/08/2013 05:06 PM, Vinod Koul wrote:
> >On Tue, Oct 08, 2013 at 03:07:59PM +0200, Lars-Peter Clausen wrote:
> >>Currently each platform making use the the generic dmaengine PCM driver still
> >>needs to provide a custom snd_pcm_hardware struct which specifies the
> >>capabilities of the DMA controller, e.g. the maximum period size that can be
> >>supported. This patch adds code which uses the newly introduced
> >>dma_get_slave_caps() API to query this information from the dmaengine driver.
> >>The new code path will only be taken if the 'pcm_hardware' field of the
> >>snd_dmaengine_pcm_config struct is NULL.
> >>
> >>The patch also introduces a new 'fifo_size' field to the
> >>snd_dmaengine_dai_dma_data struct which is used to initialize the
> >>snd_pcm_hardware 'fifo_size' field and needs to be set by the DAI driver.
> >>
> >>Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>
> >>
> >>---
> >>Changes since v1:
> >>	* Use dma_get_max_seg_size() to get the maximum size of one period
> >>	* Assume that a DMA engine driver is able to support an infinite number of
> >>	  periods
> >>	* Increase min_period_bytes from 16 to 256.
> >>---
> >>  include/sound/dmaengine_pcm.h         |  2 ++
> >>  sound/soc/soc-generic-dmaengine-pcm.c | 55 ++++++++++++++++++++++++++++-------
> >>  2 files changed, 47 insertions(+), 10 deletions(-)
> >>
> >>diff --git a/include/sound/dmaengine_pcm.h b/include/sound/dmaengine_pcm.h
> >>index f11c35c..83b2c3e 100644
> >>--- a/include/sound/dmaengine_pcm.h
> >>+++ b/include/sound/dmaengine_pcm.h
> >>@@ -61,6 +61,7 @@ struct dma_chan *snd_dmaengine_pcm_get_chan(struct snd_pcm_substream *substream)
> >>   * @slave_id: Slave requester id for the DMA channel.
> >>   * @filter_data: Custom DMA channel filter data, this will usually be used when
> >>   * requesting the DMA channel.
> >>+ * @fifo_size: FIFO size of the DAI controller in bytes
> >is this supposed to be DMA FIFO or I2S FIFO?
> 
> This field is the internal FIFO of the audio core.
> 
> >
> >And second question for Takakshi or Mark. I see that this value ends up in
> >usermode, what is the intented usage of this?
> 
> I think it is supposed to help to calculate the audio delay, but I
> don't think it is actually that widely used at the moment. And yes,
> in order to make this more accurate we should probably add support
> for incorporating also the fifo size of the DMA channel.
But then why dont add to delay field, why report to usermode

> [...]
> >>+	hw.periods_min = 2;
> >>+	hw.periods_max = UINT_MAX;
> >>+	hw.period_bytes_min = 256;
> >>+	hw.period_bytes_max = dma_get_max_seg_size(dma_dev);
> >I think you should check if the driver has set this, if not goto some default
> >
> 
> I don't think we are supposed to directly peak at the dma_parms
> field. If the DMA driver does not work with the default, and it did
> not set up a proper value, it is a bug in the DMA driver.
Well i didnt mean to peek but to check the value returned by
dma_get_max_seg_size(). Also, while buggy driver get fixed we need this :)

-- 
~Vinod