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Commit b3a223ee authored by Mark Brown's avatar Mark Brown Committed by Grant Likely
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spi: Remove SPI_BUFSIZ restriction on spi_write_then_read() 



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: default avatarMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: default avatarGrant Likely <grant.likely@secretlab.ca>
parent 266904c7

drivers/spi/spi.c

+11 −13
Original line number Diff line number Diff line
@@ -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;