spi: spidev: mask SPI_CS_HIGH in SPI_IOC_RD_MODE

Commit f3186dd8 ("spi: Optionally use GPIO descriptors for CS GPIOs")
has changed the user-space interface so that bogus SPI_CS_HIGH started
to appear in the mask returned by SPI_IOC_RD_MODE even for active-low CS
pins. Commit 138c9c32
("spi: spidev: Fix CS polarity if GPIO descriptors are used") fixed only
SPI_IOC_WR_MODE part of the problem. Let's fix SPI_IOC_RD_MODE
symmetrically.

Test case:

	#include <sys/ioctl.h>
	#include <fcntl.h>
	#include <linux/spi/spidev.h>

	int main(int argc, char **argv)
	{
		char modew = SPI_CPHA;
		char moder;
		int f = open("/dev/spidev0.0", O_RDWR);

		if (f < 0)
			return 1;

		ioctl(f, SPI_IOC_WR_MODE, &modew);
		ioctl(f, SPI_IOC_RD_MODE, &moder);

		return moder == modew ? 0 : 2;
	}

Fixes: f3186dd8 ("spi: Optionally use GPIO descriptors for CS GPIOs")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://lore.kernel.org/r/20221130162927.539512-1-alexander.sverdlin@siemens.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spidev.c

@@ -377,11 +377,22 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	switch (cmd) {
 	/* read requests */
 	case SPI_IOC_RD_MODE:
-		retval = put_user(spi->mode & SPI_MODE_MASK,
-					(__u8 __user *)arg);
-		break;
 	case SPI_IOC_RD_MODE32:
-		retval = put_user(spi->mode & SPI_MODE_MASK,
+		tmp = spi->mode;
+
+		{
+			struct spi_controller *ctlr = spi->controller;
+
+			if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
+			    ctlr->cs_gpiods[spi->chip_select])
+				tmp &= ~SPI_CS_HIGH;
+		}
+
+		if (cmd == SPI_IOC_RD_MODE)
+			retval = put_user(tmp & SPI_MODE_MASK,
+					  (__u8 __user *)arg);
+		else
+			retval = put_user(tmp & SPI_MODE_MASK,
 					  (__u32 __user *)arg);
 		break;
 	case SPI_IOC_RD_LSB_FIRST: