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spi: davinci: add comment about dummy tx buffer usage
[sfrench/cifs-2.6.git]
/
drivers
/
spi
/
spi-davinci.c
diff --git
a/drivers/spi/spi-davinci.c
b/drivers/spi/spi-davinci.c
index f37bbdd18d61772cf388d45d5327dcef556e803c..595acdcfc7d0832fbe7ef1b232e039b005788541 100644
(file)
--- a/
drivers/spi/spi-davinci.c
+++ b/
drivers/spi/spi-davinci.c
@@
-660,7
+660,11
@@
static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
goto err_desc;
if (!t->tx_buf) {
goto err_desc;
if (!t->tx_buf) {
- /* use rx buffer as dummy tx buffer */
+ /* To avoid errors when doing rx-only transfers with
+ * many SG entries (> 20), use the rx buffer as the
+ * dummy tx buffer so that dma reloads are done at the
+ * same time for rx and tx.
+ */
t->tx_sg.sgl = t->rx_sg.sgl;
t->tx_sg.nents = t->rx_sg.nents;
}
t->tx_sg.sgl = t->rx_sg.sgl;
t->tx_sg.nents = t->rx_sg.nents;
}