[patch 2.6.26 and earlier] pxa2xx_spi: bugfix full duplex dma data corruption

[Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>]

From: Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>

Fixes a data corruption bug in pxa2xx_spi.c when operating in full
duplex mode with DMA and using buffers that overlap.

SPI transmit and receive buffers are allowed to be the same or to
overlap.  However, this driver fails if such overlap is attempted in
DMA mode because it maps the rx and tx buffers in the wrong order.  By
mapping DMA_FROM_DEVICE (read) before DMA_TO_DEVICE (write), it
invalidates the cache before flushing it, thus discarding data which
should have been transmitted.

The patch corrects the order of mapping.  This bug exists in all
versions of pxa2xx_spi.c; similar bugs are in the drivers for two
other SPI controllers (au1500, imx).

This patch has been tested on kernel 2.6.20 using verification of 
loopback data with: random transfer length, random bits-per-word, 
random positive offsets (both larger and smaller than transfer length) 
between the start of the rx and tx buffers, and varying clock rates.

This patch applies to all kernels from 2.6.17 t 2.6.26.

Signed-off-by: Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>
Cc: Vernon Sauder <vernoninhand-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: J. Scott Merritt <merrij3-IL7dBOYR4Vg@public.gmane.org>
Cc: Stephen Street <stephen-nl6u4wocdmy51APUEpUfAkEOCMrvLtNR@public.gmane.org>

---

 drivers/spi/pxa2xx_spi.c |   24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff -Nurp linux-2.6.20/drivers/spi/pxa2xx_spi.c linux-2.6.20_dma_overlap_patch/drivers/spi/pxa2xx_spi.c
--- linux-2.6.20/drivers/spi/pxa2xx_spi.c	2007-02-04 18:44:54.000000000 +0000
+++ linux-2.6.20_dma_overlap_patch/drivers/spi/pxa2xx_spi.c	2008-11-17 18:21:57.000000000 +0000
@@ -334,21 +334,21 @@ static int map_dma_buffers(struct driver
 	} else
 		drv_data->tx_map_len = drv_data->len;
 
-	/* Stream map the rx buffer */
-	drv_data->rx_dma = dma_map_single(dev, drv_data->rx,
-						drv_data->rx_map_len,
-						DMA_FROM_DEVICE);
-	if (dma_mapping_error(drv_data->rx_dma))
-		return 0;
-
-	/* Stream map the tx buffer */
+	/* Stream map the tx buffer. Always do DMA_TO_DEVICE first
+	 * so we flush the cache *before* invalidating it, in case
+	 * the tx and rx buffers overlap.
+	 */
 	drv_data->tx_dma = dma_map_single(dev, drv_data->tx,
-						drv_data->tx_map_len,
-						DMA_TO_DEVICE);
+					drv_data->tx_map_len, DMA_TO_DEVICE);
+	if (dma_mapping_error(drv_data->tx_dma))
+		return 0;
 
-	if (dma_mapping_error(drv_data->tx_dma)) {
-		dma_unmap_single(dev, drv_data->rx_dma,
+	/* Stream map the rx buffer */
+	drv_data->rx_dma = dma_map_single(dev, drv_data->rx,
 					drv_data->rx_map_len, DMA_FROM_DEVICE);
+	if (dma_mapping_error(drv_data->rx_dma)) {
+		dma_unmap_single(dev, drv_data->tx_dma,
+					drv_data->tx_map_len, DMA_TO_DEVICE);
 		return 0;
 	}

-- 


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