In order to avoid constantly allocating and deallocating there is a fixed
buffer which spi_write_then_read() uses for transfers, with an early error
check to ensure that the transfer fits within the buffer. This limits the
size of transfers to this size, currently max(32, SMP_CACHE_BYTES).
Since we can dynamically allocate and in fact already have a fallback
to do so when there is contention for the fixed buffer remove this
restriction and instead dynamically allocate a suitably sized buffer if
the transfer won't fit.
Signed-off-by: Mark Brown <broo...@opensource.wolfsonmicro.com>
---
drivers/spi/spi.c | 24 +++++++++++-------------
1 file changed, 11 insertions(+), 13 deletions(-)
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index c4f7d71..224b7bc 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1646,12 +1646,18 @@ int spi_write_then_read(struct spi_device *spi,
struct spi_transfer x[2];
u8 *local_buf;
- /* Use preallocated DMA-safe buffer. We can't avoid copying here,
- * (as a pure convenience thing), but we can keep heap costs
- * out of the hot path ...
+ /* Use preallocated DMA-safe buffer if we can. We can't avoid
+ * copying here, (as a pure convenience thing), but we can
+ * keep heap costs out of the hot path unless someone else is
+ * using the pre-allocated buffer or the transfer is too large.
*/
- if ((n_tx + n_rx) > SPI_BUFSIZ)
- return -EINVAL;
+ if ((n_tx + n_rx) > SPI_BUFSIZ || !mutex_trylock(&lock)) {
+ local_buf = kmalloc(max(SPI_BUFSIZ, n_tx + n_rx), GFP_KERNEL);
+ if (!local_buf)
+ return -ENOMEM;
+ } else {
+ local_buf = buf;
+ }
spi_message_init(&message);
memset(x, 0, sizeof x);
@@ -1664,14 +1670,6 @@ int spi_write_then_read(struct spi_device *spi,
spi_message_add_tail(&x[1], &message);
}
- /* ... unless someone else is using the pre-allocated buffer */
- if (!mutex_trylock(&lock)) {
- local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
- if (!local_buf)
- return -ENOMEM;
- } else
- local_buf = buf;
-
memcpy(local_buf, txbuf, n_tx);
x[0].tx_buf = local_buf;
x[1].rx_buf = local_buf + n_tx;
--
1.7.10.4
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