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spi: spi_write_then_read() bugfixes

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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: David Brownell <dbrownell@users.sourceforge.net>
Cc: <stable@kernel.org>		[2.6.28.x, 2.6.29.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell 2009-04-13 14:39:57 -07:00 committed by Linus Torvalds
parent 0769c29814
commit bdff549ebe
1 changed files with 14 additions and 8 deletions
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22
drivers/spi/spi.c
View file

@ -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);