spi: spi_write_then_read() bugfixes (bdff549e) · Commits · 戴 / test

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>

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);

Admin message