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

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Message-ID: <20161103082608.4e27avywl5fmozt2@lukather>
Date:   Thu, 3 Nov 2016 09:26:08 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        alsa-devel@...a-project.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-sunxi@...glegroups.com, Vinod Koul <vinod.koul@...el.com>
Subject: Re: [PATCH v2 04/14] ASoC: sun4i-codec: Increase DMA max burst to 8

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@...el.com>
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

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

Thanks,
Maxime

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

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