spi: spidev: Fix CS polarity if GPIO descriptors are used

Commit f3186dd ("spi: Optionally use GPIO descriptors for CS GPIOs")
amended of_spi_parse_dt() to always set SPI_CS_HIGH for SPI slaves whose
Chip Select is defined by a "cs-gpios" devicetree property.

This change broke userspace applications which issue an SPI_IOC_WR_MODE
ioctl() to an spidev:  Chip Select polarity will be incorrect unless the
application is changed to set SPI_CS_HIGH.  And once changed, it will be
incompatible with kernels not containing the commit.

Fix by setting SPI_CS_HIGH in spidev_ioctl() (under the same conditions
as in of_spi_parse_dt()).

Fixes: f3186dd ("spi: Optionally use GPIO descriptors for CS GPIOs")
Reported-by: Simon Han <z.han@kunbus.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/fca3ba7cdc930cd36854666ceac4fbcf01b89028.1582027457.git.lukas@wunner.de
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org # v5.1+

drivers/spi/spidev.c

@@ -396,13 +396,18 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		else
 			retval = get_user(tmp, (u32 __user *)arg);
 		if (retval == 0) {
+			struct spi_controller *ctlr = spi->controller;
 			u32	save = spi->mode;
 
 			if (tmp & ~SPI_MODE_MASK) {
 				retval = -EINVAL;
 				break;
 			}
 
+			if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
+			    ctlr->cs_gpiods[spi->chip_select])
+				tmp |= SPI_CS_HIGH;
+
 			tmp |= spi->mode & ~SPI_MODE_MASK;
 			spi->mode = (u16)tmp;
 			retval = spi_setup(spi);