linux-kernel - [PATCH] pxamci: fix byte aligned DMA transfers

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Date:	Sat, 05 Jul 2008 22:00:18 +0200
From:	Philipp Zabel <philipp.zabel@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Pierre Ossman <drzeus-mmc@...eus.cx>
Cc:	Marek Vasut <marek.vasut@...il.com>
Subject: [PATCH] pxamci: fix byte aligned DMA transfers

The pxa27x DMA controller defaults to 64-bit alignment. This caused
the SCR reads to fail (and, depending on card type, error out) when
card->raw_scr was not aligned on a 8-byte boundary.

For performance reasons all scatter-gather addresses passed to
pxamci_request should be aligned on 8-byte boundaries, but if
this can't be guaranteed, byte aligned DMA transfers in the
have to be enabled in the controller to get correct behaviour.

Signed-off-by: Philipp Zabel <philipp.zabel@...il.com>
---
 drivers/mmc/host/pxamci.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/mmc/host/pxamci.c b/drivers/mmc/host/pxamci.c
index 65210fc..d89475d 100644
--- a/drivers/mmc/host/pxamci.c
+++ b/drivers/mmc/host/pxamci.c
@@ -114,6 +114,7 @@ static void pxamci_setup_data(struct pxamci_host *host, struct mmc_data *data)
 	unsigned int nob = data->blocks;
 	unsigned long long clks;
 	unsigned int timeout;
+	bool dalgn = 0;
 	u32 dcmd;
 	int i;
 
@@ -152,6 +153,9 @@ static void pxamci_setup_data(struct pxamci_host *host, struct mmc_data *data)
 		host->sg_cpu[i].dcmd = dcmd | length;
 		if (length & 31 && !(data->flags & MMC_DATA_READ))
 			host->sg_cpu[i].dcmd |= DCMD_ENDIRQEN;
+		/* Not aligned to 8-byte boundary? */
+		if (sg_dma_address(&data->sg[i]) & 0x7)
+			dalgn = 1;
 		if (data->flags & MMC_DATA_READ) {
 			host->sg_cpu[i].dsadr = host->res->start + MMC_RXFIFO;
 			host->sg_cpu[i].dtadr = sg_dma_address(&data->sg[i]);
@@ -165,6 +169,15 @@ static void pxamci_setup_data(struct pxamci_host *host, struct mmc_data *data)
 	host->sg_cpu[host->dma_len - 1].ddadr = DDADR_STOP;
 	wmb();
 
+	/*
+	 * The PXA27x DMA controller encounters overhead when working with
+	 * unaligned (to 8-byte boundaries) data, so switch on byte alignment
+	 * mode only if we have unaligned data.
+	 */
+	if (dalgn)
+		DALGN |= (1 << host->dma);
+	else
+		DALGN &= (1 << host->dma);
 	DDADR(host->dma) = host->sg_dma;
 	DCSR(host->dma) = DCSR_RUN;
 }
-- 
1.5.6


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