Re: [RFC PATCH 2/4] ASoC: soc-generic-dmaengine-pcm: Add custom prepare and submit function

[Vinod Koul <vkoul@kernel.org>]

On 17-11-20, 16:03, Michael Sit Wei Hong wrote:
> Enabling custom prepare and submit function to overcome DMA limitation.
> 
> In the Intel KeemBay solution, the DW AXI-based DMA has a limitation on
> the number of DMA blocks per transfer. In the case of 16 bit audio ASoC
> would allocate blocks exceeding the DMA block limitation.

Looking at this and cover does not tell me the limitation of the
hardware. Can you please elaborate what is the special feature this
hardware brings which results in custom solution here..?
> 
> The ASoC layers are not aware of such DMA limitation, and the DMA engine
> does not provide an API to set the maximum number of blocks per linked link.

What does a block refer to here..?

Btw have you looked into dma_slave_caps specifically max_sg_burst field
added recently

Thanks

> This patch suggests an additional callback to let the caller check and modify
> the number of blocks per transfer to work-around the limitations.
> 
> Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@intel.com>
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> ---
>  include/sound/dmaengine_pcm.h         |  6 ++++++
>  sound/core/pcm_dmaengine.c            | 30 ++++++++++++++++++++++-----
>  sound/soc/soc-generic-dmaengine-pcm.c |  8 ++++++-
>  3 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/include/sound/dmaengine_pcm.h b/include/sound/dmaengine_pcm.h
> index 8c5e38180fb0..9fae56d39ae2 100644
> --- a/include/sound/dmaengine_pcm.h
> +++ b/include/sound/dmaengine_pcm.h
> @@ -28,6 +28,9 @@ snd_pcm_substream_to_dma_direction(const struct snd_pcm_substream *substream)
>  int snd_hwparams_to_dma_slave_config(const struct snd_pcm_substream *substream,
>  	const struct snd_pcm_hw_params *params, struct dma_slave_config *slave_config);
>  int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd);
> +int snd_dmaengine_pcm_custom_trigger(struct snd_pcm_substream *substream, int cmd,
> +	int (*custom_pcm_prepare_and_submit)(struct snd_pcm_substream *substream));
> +
>  snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream);
>  snd_pcm_uframes_t snd_dmaengine_pcm_pointer_no_residue(struct snd_pcm_substream *substream);
>  
> @@ -113,6 +116,8 @@ int snd_dmaengine_pcm_refine_runtime_hwparams(
>   *   which do not use devicetree.
>   * @process: Callback used to apply processing on samples transferred from/to
>   *   user space.
> + * @custom_pcm_prepare_and_submit: Callback used to work-around DMA limitations
> + *   related to link lists.
>   * @compat_filter_fn: Will be used as the filter function when requesting a
>   *  channel for platforms which do not use devicetree. The filter parameter
>   *  will be the DAI's DMA data.
> @@ -138,6 +143,7 @@ struct snd_dmaengine_pcm_config {
>  	int (*process)(struct snd_pcm_substream *substream,
>  		       int channel, unsigned long hwoff,
>  		       void *buf, unsigned long bytes);
> +	int (*custom_pcm_prepare_and_submit)(struct snd_pcm_substream *substream);
>  	dma_filter_fn compat_filter_fn;
>  	struct device *dma_dev;
>  	const char *chan_names[SNDRV_PCM_STREAM_LAST + 1];
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index 4d059ff2b2e4..cbd1429de509 100644
> --- a/sound/core/pcm_dmaengine.c
> +++ b/sound/core/pcm_dmaengine.c
> @@ -170,16 +170,20 @@ static int dmaengine_pcm_prepare_and_submit(struct snd_pcm_substream *substream)
>  }
>  
>  /**
> - * snd_dmaengine_pcm_trigger - dmaengine based PCM trigger implementation
> + * snd_dmaengine_pcm_custom_trigger - customized PCM trigger implementation to
> + *  work-around DMA limitations related to link lists.
>   * @substream: PCM substream
>   * @cmd: Trigger command
> + * @custom_pcm_prepare_and_submit: custom function to deal with DMA limitations
>   *
>   * Returns 0 on success, a negative error code otherwise.
>   *
> - * This function can be used as the PCM trigger callback for dmaengine based PCM
> - * driver implementations.
> + * This function can be used as the PCM trigger callback for customized dmaengine
> + * based PCM driver implementations.
>   */
> -int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
> +
> +int snd_dmaengine_pcm_custom_trigger(struct snd_pcm_substream *substream, int cmd,
> +	int (*custom_pcm_prepare_and_submit)(struct snd_pcm_substream *substream))
>  {
>  	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
>  	struct snd_pcm_runtime *runtime = substream->runtime;
> @@ -187,7 +191,7 @@ int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
>  
>  	switch (cmd) {
>  	case SNDRV_PCM_TRIGGER_START:
> -		ret = dmaengine_pcm_prepare_and_submit(substream);
> +		ret = custom_pcm_prepare_and_submit(substream);
>  		if (ret)
>  			return ret;
>  		dma_async_issue_pending(prtd->dma_chan);
> @@ -214,6 +218,22 @@ int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
>  
>  	return 0;
>  }
> +EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_custom_trigger);
> +
> +/**
> + * snd_dmaengine_pcm_trigger - dmaengine based PCM trigger implementation
> + * @substream: PCM substream
> + * @cmd: Trigger command
> + *
> + * Returns 0 on success, a negative error code otherwise.
> + *
> + * This function can be used as the PCM trigger callback for dmaengine based PCM
> + * driver implementations.
> + */
> +int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
> +{
> +	return snd_dmaengine_pcm_custom_trigger(substream, cmd, dmaengine_pcm_prepare_and_submit);
> +}
>  EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_trigger);
>  
>  /**
> diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
> index 9ef80a48707e..88fca6402a36 100644
> --- a/sound/soc/soc-generic-dmaengine-pcm.c
> +++ b/sound/soc/soc-generic-dmaengine-pcm.c
> @@ -173,7 +173,13 @@ static int dmaengine_pcm_close(struct snd_soc_component *component,
>  static int dmaengine_pcm_trigger(struct snd_soc_component *component,
>  				 struct snd_pcm_substream *substream, int cmd)
>  {
> -	return snd_dmaengine_pcm_trigger(substream, cmd);
> +	struct dmaengine_pcm *pcm = soc_component_to_pcm(component);
> +
> +	if (pcm->config && pcm->config->custom_pcm_prepare_and_submit)
> +		return snd_dmaengine_pcm_custom_trigger(substream, cmd,
> +							pcm->config->custom_pcm_prepare_and_submit);
> +	else
> +		return snd_dmaengine_pcm_trigger(substream, cmd);
>  }
>  
>  static struct dma_chan *dmaengine_pcm_compat_request_channel(
> -- 
> 2.17.1

-- 
~Vinod