linux-kernel - [PATCH 4.9 21/30] serial: samsung: fix maxburst parameter for DMA transactions

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Date:   Thu, 14 Jun 2018 16:05:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: [PATCH 4.9 21/30] serial: samsung: fix maxburst parameter for DMA transactions

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marek Szyprowski <m.szyprowski@...sung.com>

commit aa2f80e752c75e593b3820f42c416ed9458fa73e upstream.

The best granularity of residue that DMA engine can report is in the BURST
units, so the serial driver must use MAXBURST = 1 and DMA_SLAVE_BUSWIDTH_1_BYTE
if it relies on exact number of bytes transferred by DMA engine.

Fixes: 62c37eedb74c ("serial: samsung: add dma reqest/release functions")
Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
Acked-by: Krzysztof Kozlowski <krzk@...nel.org>
Cc: stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/serial/samsung.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -866,15 +866,12 @@ static int s3c24xx_serial_request_dma(st
 	dma->rx_conf.direction		= DMA_DEV_TO_MEM;
 	dma->rx_conf.src_addr_width	= DMA_SLAVE_BUSWIDTH_1_BYTE;
 	dma->rx_conf.src_addr		= p->port.mapbase + S3C2410_URXH;
-	dma->rx_conf.src_maxburst	= 16;
+	dma->rx_conf.src_maxburst	= 1;
 
 	dma->tx_conf.direction		= DMA_MEM_TO_DEV;
 	dma->tx_conf.dst_addr_width	= DMA_SLAVE_BUSWIDTH_1_BYTE;
 	dma->tx_conf.dst_addr		= p->port.mapbase + S3C2410_UTXH;
-	if (dma_get_cache_alignment() >= 16)
-		dma->tx_conf.dst_maxburst = 16;
-	else
-		dma->tx_conf.dst_maxburst = 1;
+	dma->tx_conf.dst_maxburst	= 1;
 
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_SLAVE, mask);