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| -rw-r--r-- | doc/driver-model/UDM-gpio.txt | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/doc/driver-model/UDM-gpio.txt b/doc/driver-model/UDM-gpio.txt new file mode 100644 index 000000000..8ff0a965c --- /dev/null +++ b/doc/driver-model/UDM-gpio.txt @@ -0,0 +1,106 @@ +The U-Boot Driver Model Project +=============================== +GPIO analysis +============= +Viktor Krivak <viktor.krivak@gmail.com> +2012-02-24 + +I) Overview +----------- + + At this moment U-Boot provides standard API that consists of 7 functions. + + int gpio_request(unsigned gpio, const char *label) + int gpio_free(unsigned gpio) + int gpio_direction_input(unsigned gpio) + int gpio_direction_output(unsigned gpio, int value) + int gpio_get_value(unsigned gpio) + void gpio_set_value(unsigned gpio, int value) + + Methods "gpio_request()" and "gpio_free()" are used for claiming and releasing + GPIOs. First one should check if the desired pin exists and if the pin wasn't + requested already elsewhere. The method also has a label argument that can be + used for debug purposes. The label argument should be copied into the internal + memory, but only if the DEBUG macro is set. The "gpio_free()" is the exact + opposite. It releases the particular pin. Other methods are used for setting + input or output direction and obtaining or setting values of the pins. + +II) Approach +------------ + + 1) Request and free GPIO + ------------------------ + + The "gpio_request()" implementation is basically the same for all boards. + The function checks if the particular GPIO is correct and checks if the + GPIO pin is still free. If the conditions are met, the method marks the + GPIO claimed in it's internal structure. If macro DEBUG is defined, the + function also copies the label argument to the structure. If the pin is + already locked, the function returns -1 and if DEBUG is defined, certain + debug output is generated, including the contents of the label argument. + The "gpio_free()" function releases the lock and eventually deallocates + data used by the copied label argument. + + 2) Internal data + ---------------- + + Internal data are driver specific. They have to contain some mechanism to + realise the locking though. This can be done for example using a bit field. + + 3) Operations provided by the driver + ------------------------------------ + + The driver operations basically meet API that is already defined and used. + Except for "gpio_request()" and "gpio_free()", all methods can be converted in + a simple manner. The driver provides the following structure: + + struct gpio_driver_ops { + int (*gpio_request)(struct instance *i, unsigned gpio, + const char *label); + int (*gpio_free)(struct instance *i, unsigned gpio); + int (*gpio_direction_input)(struct instance *i, unsigned gpio); + int (*gpio_direction_output)(struct instance *i, unsigned gpio, + int value); + int (*gpio_get_value)(struct instance *i, unsigned gpio); + void (*gpio_set_value)(struct instance *i, unsigned gpio, int value); + } + +III) Analysis of in-tree drivers +-------------------------------- + + 1) altera_pio.c + --------------- + Meets standard API. Implements gpio_request() properly. Simple conversion + possible. + + 2) at91_gpio.c + -------------- + Don't meet standard API. Need some other methods to implement. + + 3) da8xx_gpio.c + --------------- + Meets standard API. Implements gpio_request() properly. Simple conversion + possible. + + 4) kw_gpio.c + ------------ + Doesn't meet standard API. Needs some other methods to implement and move some + methods to another file. + + 5) mpc83xx_gpio.c + ----------------- + Meets standard API. Doesn't implement gpio_request() properly (only checks + if the pin is valid). Simple conversion possible. + + 6) mvgpio.c + ----------- + Meets standard API. Doesn't implement gpio_request() properly (only checks + if the pin is valid). Simple conversion possible. + + 7) mvgpio.h + ----------- + Wrong placement. Will be moved to another location. + + 8) mvmfp.c + ---------- + Wrong placement. Will be moved to another location. |