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

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Date:   Thu,  3 Nov 2016 15:55:46 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Chen-Yu Tsai <wens@...e.org>, 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: [PATCH v2 04/14] ASoC: sun4i-codec: Increase DMA max burst to 8

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>
---
 sound/soc/sunxi/sun4i-codec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/sunxi/sun4i-codec.c b/sound/soc/sunxi/sun4i-codec.c
index 61ae502a5061..d867b96d367b 100644
--- a/sound/soc/sunxi/sun4i-codec.c
+++ b/sound/soc/sunxi/sun4i-codec.c
@@ -886,12 +886,12 @@ static int sun4i_codec_probe(struct platform_device *pdev)

 	/* DMA configuration for TX FIFO */
 	scodec->playback_dma_data.addr = res->start + quirks->reg_dac_txdata;
-	scodec->playback_dma_data.maxburst = 4;
+	scodec->playback_dma_data.maxburst = 8;
 	scodec->playback_dma_data.addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;

 	/* DMA configuration for RX FIFO */
 	scodec->capture_dma_data.addr = res->start + quirks->reg_adc_rxdata;
-	scodec->capture_dma_data.maxburst = 4;
+	scodec->capture_dma_data.maxburst = 8;
 	scodec->capture_dma_data.addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;

 	ret = snd_soc_register_codec(&pdev->dev, quirks->codec,
-- 
2.10.2