[PATCH v3 05/11] gpiolib: provide gpio_device_get_desc()

Bartosz Golaszewski
2023-09-15T15:03:46Z

Getting the GPIO descriptor directly from the gpio_chip struct is
dangerous as we don't take the reference to the underlying GPIO device.
In order to start working towards removing gpiochip_get_desc(), let's
provide a safer variant that works with an existing reference to struct
gpio_device.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
drivers/gpio/gpiolib.c | 46 +++++++++++++++++++++++++++----------
include/linux/gpio/driver.h | 2 ++
2 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 9f20311e4c1a..7d2574b3dbe5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -147,27 +147,49 @@ struct gpio_desc *gpio_to_desc(unsigned gpio)
}
EXPORT_SYMBOL_GPL(gpio_to_desc);

-/**
- * gpiochip_get_desc - get the GPIO descriptor corresponding to the given
- * hardware number for this chip
- * @gc: GPIO chip
- * @hwnum: hardware number of the GPIO for this chip
- *
- * Returns:
- * A pointer to the GPIO descriptor or ``ERR_PTR(-EINVAL)`` if no GPIO exists
- * in the given chip for the specified hardware number.
- */
+/* This function is deprecated and will be removed soon, don't use. */
struct gpio_desc *gpiochip_get_desc(struct gpio_chip *gc,
unsigned int hwnum)
{
- struct gpio_device *gdev = gc->gpiodev;
+ return gpio_device_get_desc(gc->gpiodev, hwnum);
+}
+EXPORT_SYMBOL_GPL(gpiochip_get_desc);
+
+/**
+ * gpio_device_get_desc() - get the GPIO descriptor corresponding to the given
+ * hardware number for this GPIO device
+ * @gdev: GPIO device to get the descriptor from
+ * @hwnum: hardware number of the GPIO for this chip
+ *
+ * Returns:
+ * A pointer to the GPIO descriptor or %EINVAL if no GPIO exists in the given
+ * chip for the specified hardware number or %ENODEV if the underlying chip
+ * already vanished.
+ *
+ * The reference count of struct gpio_device is *NOT* increased like when the
+ * GPIO is being requested for exclusive usage. It's up to the caller to make
+ * sure the GPIO device will stay alive together with the descriptor returned
+ * by this function.
+ */
+struct gpio_desc *
+gpio_device_get_desc(struct gpio_device *gdev, unsigned int hwnum)
+{
+ struct gpio_chip *gc;
+
+ /*
+ * FIXME: This will be locked once we protect gdev->chip everywhere
+ * with SRCU.
+ */
+ gc = gdev->chip;
+ if (!gc)
+ return ERR_PTR(-ENODEV);

if (hwnum >= gdev->ngpio)
return ERR_PTR(-EINVAL);

return &gdev->descs[hwnum];
}
-EXPORT_SYMBOL_GPL(gpiochip_get_desc);
+EXPORT_SYMBOL_GPL(gpio_device_get_desc);

/**
* desc_to_gpio - convert a GPIO descriptor to the integer namespace
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 24996cba6465..3fdf3f14bb13 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -770,6 +770,8 @@ struct gpio_desc *gpiochip_request_own_desc(struct gpio_chip *gc,
void gpiochip_free_own_desc(struct gpio_desc *desc);

struct gpio_desc *gpiochip_get_desc(struct gpio_chip *gc, unsigned int hwnum);
+struct gpio_desc *
+gpio_device_get_desc(struct gpio_device *gdev, unsigned int hwnum);

#ifdef CONFIG_GPIOLIB

--
2.39.2