linux-kernel - [PATCH 3/3] dma: edma: Increase maximum SG limit to 20

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Date:	Mon, 23 Sep 2013 18:05:15 -0500
From:	Joel Fernandes <joelf@...com>
To:	Matt Porter <matt@...orter.com>, Vinod Koul <vinod.koul@...el.com>,
	Mark Brown <broonie@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <djbw@...com>, Jyri Sarha <jsarha@...com>,
	Lars Peter-Clausen <lars@...afoo.de>
CC:	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<alsa-devel@...a-project.org>, Joel Fernandes <joelf@...com>
Subject: [PATCH 3/3] dma: edma: Increase maximum SG limit to 20

davinci-pcm uses 16 as the no.of periods. With this, in EDMA we have to
allocate atleast 17 slots: 1 slot for channel, and 16 slots the periods.

Due to this, the MAX_NR_SG limitation causes problems, set it to 20 to make
cyclic DMA work when davinci-pcm is converted to use DMA Engine. Also add
a comment clarifying this.

Signed-off-by: Joel Fernandes <joelf@...com>
---
 drivers/dma/edma.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 9b63e1e..407b496 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -46,8 +46,14 @@
 #define EDMA_CHANS	64
 #endif /* CONFIG_ARCH_DAVINCI_DA8XX */
 
-/* Max of 16 segments per channel to conserve PaRAM slots */
-#define MAX_NR_SG		16
+/*
+ * Max of 20 segments per channel to conserve PaRAM slots
+ * Also note that MAX_NR_SG should be atleast the no.of periods
+ * that are required for ASoC, otherwise DMA prep calls will
+ * fail. Today davinci-pcm is the only user of this driver and
+ * requires atleast 17 slots, so we setup the default to 20.
+ */
+#define MAX_NR_SG		20
 #define EDMA_MAX_SLOTS		MAX_NR_SG
 #define EDMA_DESCRIPTORS	16
 
-- 
1.8.1.2

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