[PATCH v3 2/2] gpio: regmap: Don't set a fixed direction line

[Linus Walleij <linusw@kernel.org>]

If a GPIO line has a fixed direction, report an error
is a consumer anyway tries to set the direction to
something other than what it is hardcoded to.

This didn't happen much before because what we supported was
all lines input or output and then the implementer would
probably not specify the direction registers, but with
sparse fixed direction we can have a mixture so let's take
this into account.

As a consequence, since gpio_regmap_set_direction() can
now fail, alter the semantics in
gpio_regmap_direction_output() such that we first check
if we can set the direction to output before we set the
value and the direction.

Suggested-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260507-regmap-gpio-sparse-fixed-dir-v1-1-a2e5855e2701%40kernel.org
Signed-off-by: Linus Walleij <linusw@kernel.org>
---
 drivers/gpio/gpio-regmap.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-regmap.c
index b3b4e77ec147..51b4d69b8740 100644
--- a/drivers/gpio/gpio-regmap.c
+++ b/drivers/gpio/gpio-regmap.c
@@ -196,6 +196,22 @@ static int gpio_regmap_get_direction(struct gpio_chip *chip,
 		return GPIO_LINE_DIRECTION_IN;
 }
 
+static int gpio_regmap_try_direction_fixed(struct gpio_regmap *gpio,
+					   unsigned int offset, bool output)
+{
+	if (test_bit(offset, gpio->fixed_direction_output)) {
+		if (output)
+			return 0;
+		else
+			return -EINVAL;
+	} else {
+		if (output)
+			return -EINVAL;
+		else
+			return 0;
+	}
+}
+
 static int gpio_regmap_set_direction(struct gpio_chip *chip,
 				     unsigned int offset, bool output)
 {
@@ -203,6 +219,13 @@ static int gpio_regmap_set_direction(struct gpio_chip *chip,
 	unsigned int base, val, reg, mask;
 	int invert, ret;
 
+	/*
+	 * If the direction is fixed, only accept the fixed
+	 * direction in this call.
+	 */
+	if (gpio_regmap_fixed_direction(gpio, offset))
+		return gpio_regmap_try_direction_fixed(gpio, offset, output);
+
 	if (gpio->reg_dir_out_base) {
 		base = gpio_regmap_addr(gpio->reg_dir_out_base);
 		invert = 0;
@@ -234,6 +257,20 @@ static int gpio_regmap_direction_input(struct gpio_chip *chip,
 static int gpio_regmap_direction_output(struct gpio_chip *chip,
 					unsigned int offset, int value)
 {
+	struct gpio_regmap *gpio = gpiochip_get_data(chip);
+	int ret;
+
+	/*
+	 * First check if this is gonna work on a fixed direction line,
+	 * if it doesn't (i.e. this is a fixed input line), then do not
+	 * attempt to set the output value either and just bail out.
+	 */
+	if (gpio_regmap_fixed_direction(gpio, offset)) {
+		ret = gpio_regmap_try_direction_fixed(gpio, offset, true);
+		if (ret)
+			return ret;
+	}
+
 	gpio_regmap_set(chip, offset, value);
 
 	return gpio_regmap_set_direction(chip, offset, true);

-- 
2.54.0