Re: [PATCH v2 04/14] ASoC: sun4i-codec: Increase DMA max burst to 8

Maxime Ripard
2016-11-03T08:26:08Z

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On Thu, Nov 03, 2016 at 03:55:46PM +0800, Chen-Yu Tsai wrote:
> According to the DMA engine API documentation, maxburst denotes the
> largest possible size of a single transfer, so as not to overflow
> destination FIFOs as explained in this excerpt from dmaengine.h
>
> * @src_maxburst: the maximum number of words (note: words, as in
> * units of the src_addr_width member, not bytes) that can be sent
> * in one burst to the device. Typically something like half the
> * FIFO depth on I/O peripherals so you don't overflow it. This
> * may or may not be applicable on memory sources.
> * @dst_maxburst: same as src_maxburst but for destination target
> * mutatis mutandis.
>
> The TX FIFO is 64 samples deep for stereo, and the RX FIFO is 16
> samples deep. So maxburst could be 32 and 8 for TX and RX respectively.
>
> Unfortunately the sunxi DMA controller driver takes maxburst as
> the requested burst size, rather than a limit, and returns an error
> for unsupported values. The original value was 4, but some later
> SoCs do not officially support this burst size.
>
> This patch increases maxburst on the TX side to 8, which is supported
> by all variants of the sunxi DMA controller.
>
> Cc: Vinod Koul <vinod.koul@intel.com>
> Signed-off-by: Chen-Yu Tsai <wens@csie.org>

Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Thanks,
Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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