Re: [PATCH 1/3] ASoC: soc-generic-dmaengine-pcm: add option to start DMA after DAI

[Lars-Peter Clausen]

On 2/16/23 01:49, Claudiu.Beznea@xxxxxxxxxxxxx wrote:
> On 14.02.2023 23:26, Mark Brown wrote:
> > On Tue, Feb 14, 2023 at 10:14:28AM -0800, Lars-Peter Clausen wrote:
> > > On 2/14/23 08:14, Claudiu Beznea wrote:
> > > > @@ -450,6 +450,8 @@ int snd_dmaengine_pcm_register(struct device *dev,
> > > >    	else
> > > >    		driver = &dmaengine_pcm_component;
> > > > +	driver->start_dma_last = config->start_dma_last;
> > > This will break if you have multiple sound cards in the system.
> > > dmaengine_pcm_component must stay const.
> > Right, if we need to modify it we either need to select which of
> > multiple const structs to register or to take a copy and modify
> > that.  I've not looked at the actual changes yet.
> OK, I will try that and return with a new patch.
>
> On the other hand do you think the other solution presented in cover letter
> would be better? From the cover letter:
>
> "The other solution that was identified for this was to extend the already
> existing mechanism around struct snd_soc_dai_link::stop_dma_first. The downside
> of this was that a potential struct snd_soc_dai_link::start_dma_last
> would have to be populated on sound card driver thus, had to be taken
> into account in all sound card drivers. At the moment, the mchp-pdmc is
> used only with simple-audio-card. In case of simple-audio-card a new DT
> binding would had to be introduced to specify this action on dai-link
> descriptions (as of my investigation)."
Can't you just set `start_dma_last` on the `mchp_pdmc_dai_component`? In 
your code you iterate over all the components of the link and if any of 
them has it set the DMA is started last.