Re: [PATCH] dma: add support for reporting pause and resume separately

[Vinod <vkoul@kernel.org>]

Hi Marek,

On 02-07-18, 15:08, Marek Szyprowski wrote:
> 'cmd_pause' DMA channel capability means that respective DMA engine
> supports both pausing and resuming given DMA channel. However, in some
> cases it is important to know if DMA channel can be paused without the
> need to resume it. This is a typical requirement for proper residue
> reading on transfer timeout in UART drivers. There are also some DMA
> engines with limited hardware, which doesn't really support resuming.

Am curious given that your hardware does not support resume, what was motivation
for adding pause?

> Reporting pause and resume capabilities separately allows UART drivers to
> properly check for the really required capabilities and operate in DMA
> mode also in systems with limited DMA hardware. On the other hand drivers,
> which rely on full channel suspend/resume support, should now check for
> both 'pause' and 'resume' features.
> 
> Existing clients of dma_get_slave_caps() have been checked and the only
> driver which rely on proper channel resuming is soc-generic-dmaengine-pcm
> driver, which has been updated to check the newly added capability.
> Existing 'cmd_pause' now only indicates that DMA engine support pausing
> given DMA channel.

The change looks fine to me. I was hoping that serial would also check
this..

Mark, Lars you okay with this?

> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> This patch is a follow-up of the Vinod's advise from the following
> discussion:
> https://www.spinics.net/lists/linux-samsung-soc/msg63166.html
> ---
>  drivers/dma/dmaengine.c               | 8 ++------
>  include/linux/dmaengine.h             | 5 ++++-
>  sound/soc/soc-generic-dmaengine-pcm.c | 2 +-
>  3 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 08ba8473a284..84ac38dbdb65 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -500,12 +500,8 @@ int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
>  	caps->max_burst = device->max_burst;
>  	caps->residue_granularity = device->residue_granularity;
>  	caps->descriptor_reuse = device->descriptor_reuse;
> -
> -	/*
> -	 * Some devices implement only pause (e.g. to get residuum) but no
> -	 * resume. However cmd_pause is advertised as pause AND resume.
> -	 */
> -	caps->cmd_pause = !!(device->device_pause && device->device_resume);
> +	caps->cmd_pause = !!device->device_pause;
> +	caps->cmd_resume = !!device->device_resume;
>  	caps->cmd_terminate = !!device->device_terminate_all;
>  
>  	return 0;
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 861be5cab1df..c8c3a7a93802 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -415,7 +415,9 @@ enum dma_residue_granularity {
>   *	each type, the dma controller should set BIT(<TYPE>) and same
>   *	should be checked by controller as well
>   * @max_burst: max burst capability per-transfer
> - * @cmd_pause: true, if pause and thereby resume is supported
> + * @cmd_pause: true, if pause is supported (i.e. for reading residue or
> + *	       for resume later)
> + * @cmd_resume: true, if resume is supported
>   * @cmd_terminate: true, if terminate cmd is supported
>   * @residue_granularity: granularity of the reported transfer residue
>   * @descriptor_reuse: if a descriptor can be reused by client and
> @@ -427,6 +429,7 @@ struct dma_slave_caps {
>  	u32 directions;
>  	u32 max_burst;
>  	bool cmd_pause;
> +	bool cmd_resume;
>  	bool cmd_terminate;
>  	enum dma_residue_granularity residue_granularity;
>  	bool descriptor_reuse;
> diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
> index 56a541b9ff9e..76c46d793843 100644
> --- a/sound/soc/soc-generic-dmaengine-pcm.c
> +++ b/sound/soc/soc-generic-dmaengine-pcm.c
> @@ -156,7 +156,7 @@ static int dmaengine_pcm_set_runtime_hwparams(struct snd_pcm_substream *substrea
>  
>  	ret = dma_get_slave_caps(chan, &dma_caps);
>  	if (ret == 0) {
> -		if (dma_caps.cmd_pause)
> +		if (dma_caps.cmd_pause && dma_caps.cmd_resume)
>  			hw.info |= SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME;
>  		if (dma_caps.residue_granularity <= DMA_RESIDUE_GRANULARITY_SEGMENT)
>  			hw.info |= SNDRV_PCM_INFO_BATCH;
> -- 
> 2.17.1
> 
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-- 
~Vinod