staging: fbtft: Do not hardcode SPI CS polarity inversion
The current use of the mode flag SPI_CS_HIGH is fragile: it
overwrites anything already assigned by the SPI core.
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>
Link: https://lore.kernel.org/r/20191204233230.22309-1-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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