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spi: Fix zero length xfer bug 

This fixes a bug for messages containing both zero length and
unidirectional xfers.

The function spi_map_msg will allocate dummy tx and/or rx buffers
for use with unidirectional transfers when the hardware can only do
a bidirectional transfer.  That dummy buffer will be used in place
of a NULL buffer even when the xfer length is 0.

Then in the function __spi_map_msg, if he hardware can dma,
the zero length xfer will have spi_map_buf called on the dummy
buffer.

Eventually, __sg_alloc_table is called and returns -EINVAL
because nents == 0.

This fix prevents the error by not using the dummy buffer when
the xfer length is zero.

Signed-off-by: Chris Lesiak <chris.lesiak@licor.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Chris Lesiak 2019-03-07 20:39:00 +00:00 committed by Mark Brown
parent 0e836c3bea
commit 5442dcaa0d
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1 changed files with 2 additions and 0 deletions
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2
drivers/spi/spi.c
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@ -1039,6 +1039,8 @@ static int spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
if (max_tx || max_rx) {
list_for_each_entry(xfer, &msg->transfers,
transfer_list) {
if (!xfer->len)
continue;
if (!xfer->tx_buf)
xfer->tx_buf = ctlr->dummy_tx;
if (!xfer->rx_buf)