Applied "spi: Fix zero length xfer bug" to the spi tree

[Mark Brown <broonie@xxxxxxxxxx>]

The patch

   spi: Fix zero length xfer bug

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 5442dcaa0d90fc376bdfc179a018931a8f43dea4 Mon Sep 17 00:00:00 2001
From: Chris Lesiak <chris.lesiak@xxxxxxxxx>
Date: Thu, 7 Mar 2019 20:39:00 +0000
Subject: [PATCH] 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@xxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 drivers/spi/spi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 93986f879b09..2be394d3bc59 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -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)
-- 
2.20.1