linux-kernel - [PATCH] mfd: mc13xxx-spi: Do not hardcode SPI mode flags

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Date:   Wed,  4 Dec 2019 16:27:15 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     lee.jones@...aro.org, linux-kernel@...r.kernel.org
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>
Subject: [PATCH] mfd: mc13xxx-spi: Do not hardcode SPI mode flags

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@...nel.org>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 drivers/mfd/mc13xxx-spi.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/mc13xxx-spi.c b/drivers/mfd/mc13xxx-spi.c
index 286ddcf5ddc6..9885e5f8210a 100644
--- a/drivers/mfd/mc13xxx-spi.c
+++ b/drivers/mfd/mc13xxx-spi.c
@@ -134,7 +134,13 @@ static int mc13xxx_spi_probe(struct spi_device *spi)
 
 	dev_set_drvdata(&spi->dev, mc13xxx);
 
-	spi->mode = SPI_MODE_0 | SPI_CS_HIGH;
+	spi->mode |= SPI_MODE_0;
+	/*
+	 * We want the inverse of what is set in the SPI core, if this
+	 * is accomplished with a GPIO line then inversion semantics may
+	 * be handled in the GPIO library.
+	 */
+	spi->mode ^= SPI_CS_HIGH;
 
 	mc13xxx->irq = spi->irq;
 
-- 
2.23.0