linux-kernel - [PATCH] spi: spidev: mask SPI_CS_HIGH in SPI_IOC_RD

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Message-Id: <20221130143948.426640-1-alexander.sverdlin@siemens.com>
Date:   Wed, 30 Nov 2022 15:39:48 +0100
From:   "A. Sverdlin" <alexander.sverdlin@...mens.com>
To:     linux-spi@...r.kernel.org
Cc:     Alexander Sverdlin <alexander.sverdlin@...mens.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Lukas Wunner <lukas@...ner.de>
Subject: [PATCH] spi: spidev: mask SPI_CS_HIGH in SPI_IOC_RD_MODE

From: Alexander Sverdlin <alexander.sverdlin@...mens.com>

Commit f3186dd87669 ("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 138c9c32f090
("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: f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
---
 drivers/spi/spidev.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index b2775d82d2d7b..23177a7c916c3 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -377,8 +377,17 @@ 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);
+		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;
+		}
+
+		retval = put_user(tmp & SPI_MODE_MASK, (__u8 __user *)arg);
 		break;
 	case SPI_IOC_RD_MODE32:
 		retval = put_user(spi->mode & SPI_MODE_MASK,
-- 
2.34.1