linux-kernel - Re: [PATCH 2/2] ASoC: bcm2835: Add S16_LE support via packed DMA transfers

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Date:	Wed, 27 Apr 2016 16:33:14 +0200
From:	Martin Sperl <kernel@...tin.sperl.org>
To:	Matthias Reichl <hias@...us.com>
Cc:	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>, Eric Anholt <eric@...olt.net>,
	Luis de Bethencourt <luis@...ethencourt.com>,
	alsa-devel@...a-project.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ASoC: bcm2835: Add S16_LE support via packed DMA transfers


> On 27.04.2016, at 15:26, Matthias Reichl <hias@...us.com> wrote:
> 
> The bcm2835-i2s driver already has support for the S16_LE format but
> that format hasn't been made available because dmaengine_pcm didn't
> support packed data transfers.
> 
> bcm2835-i2s needs 16-bit left+right channel data to be packed into
> a 32-bit word, the FIFO register is 32-bit only and doesn't support
> 16-bit access.
> 
> Now that dmaengine_pcm supports packed transfers the format can
> be made available by setting the SND_DMAENGINE_PCM_DAI_FLAG_PACK flag.
> 
> No further configuration is necessary:
> - snd_dmaengine_dai_dma_data.addr_width is already set to
>  DMA_SLAVE_BUSWIDTH_4_BYTES to force 32-bit DMA transfers
> - dmaengine_pcm will pick up the S16_LE format from the DAI
>  configuration and make it available since it's no longer
>  masked out due to the PACK flag.
> - there are no further corner cases to catch in hw_params,
>  since the channel count is fixed at 2 we always have two
>  16-bit stereo samples that can be transferred via 32-bit DMA
> 
> Signed-off-by: Matthias Reichl <hias@...us.com>

Tested-by: Martin Sperl <kernel@...tin.sperl.org>