Because the dma_map_single() on ARM only flushes and invalidates
the cache-lines occupied by the transfer buffer, care should be
taken not to touch memory that share the same cache-lines before
starting the DMA transfer.
In the McSPI driver dma_map_single() was called before the driver
was finished touching the spi_message and spi_transfer structures,
causing potential corruption of the transfer buffer.
With a layout like this:
struct spi_message read_msg;
u16 data[4];
- my (touchscreen) driver would get
[ 5.875000] 0 0 1002 3334
[ 6.695312] 0 0 1363 3234
after playing with the layout so that data[] starts on
a new cache-line I would get:
[ 5.890625] 1507 788 1278 2720
[ 5.890625] 1507 819 1242 2779
This patch solves the problem by moving the dma_map_single()
calls to just before the DMA is started.
Signed-off-by: Klaus Pedersen <klaus.k.pedersen@xxxxxxxxx>
---
drivers/spi/omap2_mcspi.c | 48 +++++++++++++++++++-------------------------
1 files changed, 21 insertions(+), 27 deletions(-)
diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c
index a6ba11a..987a472 100644
--- a/drivers/spi/omap2_mcspi.c
+++ b/drivers/spi/omap2_mcspi.c
@@ -251,6 +251,15 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
}
if (tx != NULL) {
+ xfer->tx_dma = dma_map_single(&spi->dev, (void *)tx, count,
+ DMA_TO_DEVICE);
+ if (dma_mapping_error(xfer->tx_dma)) {
+ dev_err(&spi->dev,
+ "%s(): Couldn't DMA map a %d bytes %cX buffer\n",
+ __FUNCTION__, 'T', count);
+ return 0;
+ }
+
omap_set_dma_transfer_params(mcspi_dma->dma_tx_channel,
data_type, element_count, 1,
OMAP_DMA_SYNC_ELEMENT,
@@ -266,6 +275,18 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
}
if (rx != NULL) {
+ xfer->rx_dma = dma_map_single(&spi->dev, rx, count,
+ DMA_FROM_DEVICE);
+ if (dma_mapping_error(xfer->rx_dma)) {
+ dev_err(&spi->dev,
+ "%s(): Couldn't DMA map a %d bytes %cX buffer\n",
+ __FUNCTION__, 'T', count);
+ if (tx != NULL)
+ dma_unmap_single(NULL, xfer->tx_dma,
+ count, DMA_TO_DEVICE);
+ return 0;
+ }
+
omap_set_dma_transfer_params(mcspi_dma->dma_rx_channel,
data_type, element_count, 1,
OMAP_DMA_SYNC_ELEMENT,
@@ -827,33 +848,6 @@ static int omap2_mcspi_transfer(struct spi_device *spi, struct spi_message *m)
if (m->is_dma_mapped || len < DMA_MIN_BYTES)
continue;
-
- /* Do DMA mapping "early" for better error reporting and
- * dcache use. Note that if dma_unmap_single() ever starts
- * to do real work on ARM, we'd need to clean up mappings
- * for previous transfers on *ALL* exits of this loop...
- */
- if (tx_buf != NULL) {
- t->tx_dma = dma_map_single(&spi->dev, (void *) tx_buf,
- len, DMA_TO_DEVICE);
- if (dma_mapping_error(t->tx_dma)) {
- dev_dbg(&spi->dev, "dma %cX %d bytes error\n",
- 'T', len);
- return -EINVAL;
- }
- }
- if (rx_buf != NULL) {
- t->rx_dma = dma_map_single(&spi->dev, rx_buf, t->len,
- DMA_FROM_DEVICE);
- if (dma_mapping_error(t->rx_dma)) {
- dev_dbg(&spi->dev, "dma %cX %d bytes error\n",
- 'R', len);
- if (tx_buf != NULL)
- dma_unmap_single(NULL, t->tx_dma,
- len, DMA_TO_DEVICE);
- return -EINVAL;
- }
- }
}
mcspi = spi_master_get_devdata(spi->master);
--
1.5.3.3
-
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