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Subject[PATCH] pxamci: fix byte aligned DMA transfers
From: Philipp Zabel <philipp.zabel@gmail.com>

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@gmail.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
---
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;
}

--
-- Pierre Ossman

Linux kernel, MMC maintainer http://www.kernel.org
rdesktop, core developer http://www.rdesktop.org

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