gpio: reinforce desc->flags handling

We now removed the gpio_lock spinlock and modified the places
previously protected by it to handle desc->flags access in a consistent
way. Let's improve other places that were previously unprotected by
reading the flags field of gpio_desc once and using the stored value for
logic consistency. If we need to modify the field, let's also write it
back once with a consistent value resulting from the function's logic.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpiolib.c

@@ -336,18 +336,20 @@ static int gpiochip_find_base_unlocked(int ngpio)
 int gpiod_get_direction(struct gpio_desc *desc)
 {
 	struct gpio_chip *gc;
+	unsigned long flags;
 	unsigned int offset;
 	int ret;
 
 	gc = gpiod_to_chip(desc);
 	offset = gpio_chip_hwgpio(desc);
+	flags = READ_ONCE(desc->flags);
 
 	/*
 	 * Open drain emulation using input mode may incorrectly report
 	 * input here, fix that up.
 	 */
-	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags) &&
-	    test_bit(FLAG_IS_OUT, &desc->flags))
+	if (test_bit(FLAG_OPEN_DRAIN, &flags) &&
+	    test_bit(FLAG_IS_OUT, &flags))
 		return 0;
 
 	if (!gc->get_direction)
@@ -361,7 +363,8 @@ int gpiod_get_direction(struct gpio_desc *desc)
 	if (ret > 0)
 		ret = 1;
 
-	assign_bit(FLAG_IS_OUT, &desc->flags, !ret);
+	assign_bit(FLAG_IS_OUT, &flags, !ret);
+	WRITE_ONCE(desc->flags, flags);
 
 	return ret;
 }
@@ -751,9 +754,6 @@ static void gpiochip_machine_hog(struct gpio_chip *gc, struct gpiod_hog *hog)
 		return;
 	}
 
-	if (test_bit(FLAG_IS_HOGGED, &desc->flags))
-		return;
-
 	rv = gpiod_hog(desc, hog->line_name, hog->lflags, hog->dflags);
 	if (rv)
 		gpiod_err(desc, "%s: unable to hog GPIO line (%s:%u): %d\n",
@@ -2528,13 +2528,16 @@ static int gpio_set_config(struct gpio_desc *desc, enum pin_config_param mode)
 static int gpio_set_bias(struct gpio_desc *desc)
 {
 	enum pin_config_param bias;
+	unsigned long flags;
 	unsigned int arg;
 
-	if (test_bit(FLAG_BIAS_DISABLE, &desc->flags))
+	flags = READ_ONCE(desc->flags);
+
+	if (test_bit(FLAG_BIAS_DISABLE, &flags))
 		bias = PIN_CONFIG_BIAS_DISABLE;
-	else if (test_bit(FLAG_PULL_UP, &desc->flags))
+	else if (test_bit(FLAG_PULL_UP, &flags))
 		bias = PIN_CONFIG_BIAS_PULL_UP;
-	else if (test_bit(FLAG_PULL_DOWN, &desc->flags))
+	else if (test_bit(FLAG_PULL_DOWN, &flags))
 		bias = PIN_CONFIG_BIAS_PULL_DOWN;
 	else
 		return 0;
@@ -2700,24 +2703,28 @@ EXPORT_SYMBOL_GPL(gpiod_direction_output_raw);
  */
 int gpiod_direction_output(struct gpio_desc *desc, int value)
 {
+	unsigned long flags;
 	int ret;
 
 	VALIDATE_DESC(desc);
-	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
+
+	flags = READ_ONCE(desc->flags);
+
+	if (test_bit(FLAG_ACTIVE_LOW, &flags))
 		value = !value;
 	else
 		value = !!value;
 
 	/* GPIOs used for enabled IRQs shall not be set as output */
-	if (test_bit(FLAG_USED_AS_IRQ, &desc->flags) &&
-	    test_bit(FLAG_IRQ_IS_ENABLED, &desc->flags)) {
+	if (test_bit(FLAG_USED_AS_IRQ, &flags) &&
+	    test_bit(FLAG_IRQ_IS_ENABLED, &flags)) {
 		gpiod_err(desc,
 			  "%s: tried to set a GPIO tied to an IRQ as output\n",
 			  __func__);
 		return -EIO;
 	}
 
-	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {
+	if (test_bit(FLAG_OPEN_DRAIN, &flags)) {
 		/* First see if we can enable open drain in hardware */
 		ret = gpio_set_config(desc, PIN_CONFIG_DRIVE_OPEN_DRAIN);
 		if (!ret)
@@ -2727,7 +2734,7 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
 			ret = gpiod_direction_input(desc);
 			goto set_output_flag;
 		}
-	} else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags)) {
+	} else if (test_bit(FLAG_OPEN_SOURCE, &flags)) {
 		ret = gpio_set_config(desc, PIN_CONFIG_DRIVE_OPEN_SOURCE);
 		if (!ret)
 			goto set_output_value;
@@ -4424,21 +4431,22 @@ int gpiod_hog(struct gpio_desc *desc, const char *name,
 	int hwnum;
 	int ret;
 
+	if (test_and_set_bit(FLAG_IS_HOGGED, &desc->flags))
+		return 0;
+
 	gc = gpiod_to_chip(desc);
 	hwnum = gpio_chip_hwgpio(desc);
 
 	local_desc = gpiochip_request_own_desc(gc, hwnum, name,
 					       lflags, dflags);
 	if (IS_ERR(local_desc)) {
+		clear_bit(FLAG_IS_HOGGED, &desc->flags);
 		ret = PTR_ERR(local_desc);
 		pr_err("requesting hog GPIO %s (chip %s, offset %d) failed, %d\n",
 		       name, gc->label, hwnum, ret);
 		return ret;
 	}
 
-	/* Mark GPIO as hogged so it can be identified and removed later */
-	set_bit(FLAG_IS_HOGGED, &desc->flags);
-
 	gpiod_dbg(desc, "hogged as %s%s\n",
 		(dflags & GPIOD_FLAGS_BIT_DIR_OUT) ? "output" : "input",
 		(dflags & GPIOD_FLAGS_BIT_DIR_OUT) ?