Applied "spi: gpio: No MISO does not imply no RX" to the spi tree

Commit Message

Mark Brown Sept. 10, 2018, 2:22 p.m. UTC

The patch

   spi: gpio: No MISO does not imply no RX

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 abf5feef3ff0cefade0c76be53b59e55fdd46093 Mon Sep 17 00:00:00 2001
From: Linus Walleij <[e-mail]>
Date: Mon, 10 Sep 2018 00:28:05 +0200
Subject: [PATCH] spi: gpio: No MISO does not imply no RX

There is a logical problem in spi-gpio with host just
assigning a MOSI line and no MISO: this is interpreted
as the host cannot do RX and the host is flagged with
SPI_MASTER_NO_RX.

This is wrong: since GPIO lines can switch direction,
in 3WIRE operation the host will simply reverse the
direction of the GPIO line and start reading from it,
there is even code for doing this in the driver, but
it went unnoticed because it was tested by using a
master with 4 wires but a device using just 3 wires.

Remove the offending flag.

Cc: Andrzej Hajda <[e-mail]>
Cc: Lorenzo Bianconi <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>
---
 drivers/spi/spi-gpio.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Patch

diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
index d0c6d71b6c0f..a2b08b464857 100644
--- a/drivers/spi/spi-gpio.c
+++ b/drivers/spi/spi-gpio.c
@@ -295,9 +295,11 @@  static int spi_gpio_request(struct device *dev,
 	spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
 	if (IS_ERR(spi_gpio->miso))
 		return PTR_ERR(spi_gpio->miso);
-	if (!spi_gpio->miso)
-		/* HW configuration without MISO pin */
-		*mflags |= SPI_MASTER_NO_RX;
+	/*
+	 * No setting SPI_MASTER_NO_RX here - if there is only a MOSI
+	 * pin connected the host can still do RX by changing the
+	 * direction of the line.
+	 */
 
 	spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
 	if (IS_ERR(spi_gpio->mosi))
@@ -423,7 +425,7 @@  static int spi_gpio_probe(struct platform_device *pdev)
 	spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
 	spi_gpio->bitbang.set_line_direction = spi_gpio_set_direction;
 
-	if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
+	if ((master_flags & SPI_MASTER_NO_TX) == 0) {
 		spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
 		spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
 		spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;