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spi: Remove SPI_BUFSIZ restriction on spi_write_then_read()

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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 <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
This commit is contained in:
Mark Brown 2012-12-02 12:54:25 +09:00 • committed by Grant Likely
commit b3a223ee2d
1 changed files with 11 additions and 13 deletions
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24
drivers/spi/spi.c
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@ -1545,12 +1545,18 @@ 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);
@ -1563,14 +1569,6 @@ 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;