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From f0f4368b3497d129c0c4ca0565f5b6656faed474 Mon Sep 17 00:00:00 2001
From: Matthias Reichl <hias@horus.com>
Date: Sun, 11 Oct 2015 12:28:30 +0200
Subject: [PATCH] bcm2835-dma: Limit cyclic transfers on lite channels to 32k
Transfers larger than 32k cause repeated clicking with I2S soundcards.
The exact reason is yet unknown, so limit to 32k as bcm2708-dmaengine
did as an intermediate fix.
---
drivers/dma/bcm2835-dma.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c
@@ -144,6 +144,12 @@ struct bcm2835_desc {
*/
#define MAX_LITE_TRANSFER (SZ_64K - 4)
+/*
+ * Transfers larger than 32k cause issues with the bcm2708-i2s driver,
+ * so limit transfer size to 32k as bcm2708-dmaengine did.
+ */
+#define MAX_CYCLIC_LITE_TRANSFER SZ_32K
+
static inline struct bcm2835_dmadev *to_bcm2835_dma_dev(struct dma_device *d)
{
return container_of(d, struct bcm2835_dmadev, ddev);
@@ -412,7 +418,7 @@ static struct dma_async_tx_descriptor *b
d->c = c;
d->dir = direction;
if (c->ch >= 8) /* LITE channel */
- max_size = MAX_LITE_TRANSFER;
+ max_size = MAX_CYCLIC_LITE_TRANSFER;
else
max_size = MAX_NORMAL_TRANSFER;
period_len = min(period_len, max_size);
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