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

From: Lars-Peter Clausen <lars@metafoo.de>
To: Claudiu.Beznea@microchip.com, broonie@kernel.org
Cc: devicetree@vger.kernel.org, alexandre.belloni@bootlin.com,
	alsa-devel@alsa-project.org, lgirdwood@gmail.com,
	linux-kernel@vger.kernel.org, tiwai@suse.com, robh+dt@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, perex@perex.cz,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/3] ASoC: soc-generic-dmaengine-pcm: add option to start DMA after DAI
Date: Thu, 16 Feb 2023 05:53:34 -0800	[thread overview]
Message-ID: <b57b8fbe-c558-8d5d-5fb3-7540d2fa83ae@metafoo.de> (raw)
In-Reply-To: <4b109846-2019-219a-262e-46f5bb504c99@microchip.com>

On 2/16/23 01:49, Claudiu.Beznea@microchip.com 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.

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