[PATCH] mfd: motorola-cpcap: Do not hardcode SPI mode flags

Linus Walleij
2019-12-04T23:21:45Z

The current use of mode flags to us SPI_MODE_0 and
SPI_CS_HIGH is fragile: it overwrites anything already
assigned by the SPI core. Change it thusly:

- Just |= the SPI_MODE_0 so we keep other flags
- Assign ^= SPI_CS_HIGH since we might be active high
already, and that is usually the case with GPIOs used
for chip select, even if they are in practice active low.

Add a comment clarifying why ^= SPI_CS_HIGH is the right
choice here.

Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
drivers/mfd/motorola-cpcap.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/motorola-cpcap.c b/drivers/mfd/motorola-cpcap.c
index 52f38e57cdc1..a3bc61b8008c 100644
--- a/drivers/mfd/motorola-cpcap.c
+++ b/drivers/mfd/motorola-cpcap.c
@@ -279,7 +279,13 @@ static int cpcap_probe(struct spi_device *spi)
spi_set_drvdata(spi, cpcap);

spi->bits_per_word = 16;
- spi->mode = SPI_MODE_0 | SPI_CS_HIGH;
+ spi->mode |= SPI_MODE_0;
+ /*
+ * Active high should be defined as "inverse polarity" as GPIO-based
+ * chip selects can be logically active high but inverted by the GPIO
+ * library.
+ */
+ spi->mode ^= SPI_CS_HIGH;

ret = spi_setup(spi);
if (ret)
--
2.23.0