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Subject[RFC PATCH 1/5] gpio: add a vtable to abstract GPIO controller operations
Date
A common pattern to implement object oriented code in the kernel is
to use a separate structure to hold all the methods for a particular
kind of object and just have a pointer to this table rather than a
separate pointer for each method.

The alternate approach is to directly embedded function pointers in
the object but there are some advantages on using the former approach.

This patch adds a struct gpio_chip_ops to be set by GPIO chip controllers.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
---
include/linux/gpio/driver.h | 47 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 47 insertions(+)

diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 1827b43..824cd32 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -16,6 +16,51 @@ struct seq_file;
#ifdef CONFIG_GPIOLIB

/**
+ * struct gpio_chip_ops - virtual function table for GPIO controller operations
+ * @request: optional hook for chip-specific activation, such as
+ * enabling module power and clock; may sleep
+ * @free: optional hook for chip-specific deactivation, such as
+ * disabling module power and clock; may sleep
+ * @get_direction: returns direction for signal "offset", 0=out, 1=in,
+ * (same as GPIOF_DIR_XXX), or negative error
+ * @direction_input: configures signal "offset" as input, or returns error
+ * @direction_output: configures signal "offset" as output, or returns error
+ * @get: returns value for signal "offset"; for output signals this
+ * returns either the value actually sensed, or zero
+ * @set: assigns output value for signal "offset"
+ * @set_debounce: optional hook for setting debounce time for specified gpio in
+ * interrupt triggered gpio chips
+ * @dbg_show: optional routine to show contents in debugfs; default code
+ * will be used when this is omitted, but custom code can show extra
+ * state (such as pullup/pulldown configuration).
+ *
+ * A gpio_chip_ops is used as a virtual function table for gpio_chip so GPIO
+ * drivers can define their custom methods as needed by its the GPIO controller.
+ */
+struct gpio_chip_ops {
+ int (*request)(struct gpio_chip *chip,
+ unsigned offset);
+ void (*free)(struct gpio_chip *chip,
+ unsigned offset);
+ int (*get_direction)(struct gpio_chip *chip,
+ unsigned offset);
+ int (*direction_input)(struct gpio_chip *chip,
+ unsigned offset);
+ int (*direction_output)(struct gpio_chip *chip,
+ unsigned offset, int value);
+ int (*get)(struct gpio_chip *chip,
+ unsigned offset);
+ void (*set)(struct gpio_chip *chip,
+ unsigned offset, int value);
+ int (*set_debounce)(struct gpio_chip *chip,
+ unsigned offset,
+ unsigned debounce);
+
+ void (*dbg_show)(struct seq_file *s,
+ struct gpio_chip *chip);
+};
+
+/**
* struct gpio_chip - abstract a GPIO controller
* @label: for diagnostics
* @dev: optional device providing the GPIOs
@@ -44,6 +89,7 @@ struct seq_file;
* @ngpio: the number of GPIOs handled by this controller; the last GPIO
* handled is (base + ngpio - 1).
* @desc: array of ngpio descriptors. Private.
+ * @ops: virtual table with GPIO controller operations.
* @names: if set, must be an array of strings to use as alternative
* names for the GPIOs in this chip. Any entry in the array
* may be NULL if there is no alias for the GPIO, however the
@@ -97,6 +143,7 @@ struct gpio_chip {
u16 ngpio;
struct gpio_desc *desc;
const char *const *names;
+ const struct gpio_chip_ops *ops;
bool can_sleep;
bool exported;

--
1.9.0


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