diff options
| author | Kris Bahnsen | 2022-12-07 15:08:53 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2022-12-31 13:32:25 +0100 |
| commit | 9d0190d4722ae9a5be9de21fa2b3a3eb9db2bc0e (patch) | |
| tree | 3713b01bb8bb251f576e2c13eeaf64324f1c0c18 /drivers/spi | |
| parent | a35323218ff32782d051d2643912311a22e07b6a (diff) | |
spi: spi-gpio: Don't set MOSI as an input if not 3WIRE mode
[ Upstream commit 3a6f994f848a69deb2bf3cd9d130dd0c09730e55 ]
The addition of 3WIRE support would affect MOSI direction even
when still in standard (4 wire) mode. This can lead to MOSI being
at an invalid logic level when a device driver sets an SPI
message with a NULL tx_buf.
spi.h states that if tx_buf is NULL then "zeros will be shifted
out ... " If MOSI is tristated then the data shifted out is subject
to pull resistors, keepers, or in the absence of those, noise.
This issue came to light when using spi-gpio connected to an
ADS7843 touchscreen controller. MOSI pulled high when clocking
MISO data in caused the SPI device to interpret this as a command
which would put the device in an unexpected and non-functional
state.
Fixes: 4b859db2c606 ("spi: spi-gpio: add SPI_3WIRE support")
Fixes: 5132b3d28371 ("spi: gpio: Support 3WIRE high-impedance turn-around")
Signed-off-by: Kris Bahnsen <kris@embeddedTS.com>
Link: https://lore.kernel.org/r/20221207230853.6174-1-kris@embeddedTS.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-gpio.c | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c index 4b12c4964a66..9c8c7948044e 100644 --- a/drivers/spi/spi-gpio.c +++ b/drivers/spi/spi-gpio.c @@ -268,9 +268,19 @@ static int spi_gpio_set_direction(struct spi_device *spi, bool output) if (output) return gpiod_direction_output(spi_gpio->mosi, 1); - ret = gpiod_direction_input(spi_gpio->mosi); - if (ret) - return ret; + /* + * Only change MOSI to an input if using 3WIRE mode. + * Otherwise, MOSI could be left floating if there is + * no pull resistor connected to the I/O pin, or could + * be left logic high if there is a pull-up. Transmitting + * logic high when only clocking MISO data in can put some + * SPI devices in to a bad state. + */ + if (spi->mode & SPI_3WIRE) { + ret = gpiod_direction_input(spi_gpio->mosi); + if (ret) + return ret; + } /* * Send a turnaround high impedance cycle when switching * from output to input. Theoretically there should be |