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Commit bdff549e authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
Browse files

spi: spi_write_then_read() bugfixes 



The "simplify spi_write_then_read()" patch included two regressions from
the 2.6.27 behaviors:

 - The data it wrote out during the (full duplex) read side
   of the transfer was not zeroed.

 - It fails completely on half duplex hardware, such as
   Microwire and most "3-wire" SPI variants.

So, revert that patch.  A revised version should be submitted at some
point, which can get the speedup on standard hardware (full duplex)
without breaking on less-capable half-duplex stuff.

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Cc: <stable@kernel.org>		[2.6.28.x, 2.6.29.x]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0769c298

drivers/spi/spi.c

+14 −8
Original line number Diff line number Diff line
@@ -658,7 +658,7 @@ int spi_write_then_read(struct spi_device *spi, 


	int			status;

	struct spi_message	message;

	struct spi_transfer	x;

	struct spi_transfer	x[2];

	u8			*local_buf;



	/* Use preallocated DMA-safe buffer.  We can't avoid copying here,
@@ -669,9 +669,15 @@ int spi_write_then_read(struct spi_device *spi, 
		return -EINVAL;



	spi_message_init(&message);

	memset(&x, 0, sizeof x);

	x.len = n_tx + n_rx;

	spi_message_add_tail(&x, &message);

	memset(x, 0, sizeof x);

	if (n_tx) {

		x[0].len = n_tx;

		spi_message_add_tail(&x[0], &message);

	}

	if (n_rx) {

		x[1].len = n_rx;

		spi_message_add_tail(&x[1], &message);

	}



	/* ... unless someone else is using the pre-allocated buffer */

	if (!mutex_trylock(&lock)) {
@@ -682,15 +688,15 @@ int spi_write_then_read(struct spi_device *spi, 
		local_buf = buf;



	memcpy(local_buf, txbuf, n_tx);

	x.tx_buf = local_buf;

	x.rx_buf = local_buf;

	x[0].tx_buf = local_buf;

	x[1].rx_buf = local_buf + n_tx;



	/* do the i/o */

	status = spi_sync(spi, &message);

	if (status == 0)

		memcpy(rxbuf, x.rx_buf + n_tx, n_rx);

		memcpy(rxbuf, x[1].rx_buf, n_rx);



	if (x.tx_buf == buf)

	if (x[0].tx_buf == buf)

		mutex_unlock(&lock);

	else

		kfree(local_buf);