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Diffstat (limited to 'doc/driver-model/UDM-gpio.txt')
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1 files changed, 0 insertions, 106 deletions
diff --git a/doc/driver-model/UDM-gpio.txt b/doc/driver-model/UDM-gpio.txt deleted file mode 100644 index 585d458..0000000 --- a/doc/driver-model/UDM-gpio.txt +++ /dev/null @@ -1,106 +0,0 @@ -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 --------------------------------- - - altera_pio.c - ------------ - Meets standard API. Implements gpio_request() properly. Simple conversion - possible. - - at91_gpio.c - ----------- - Don't meet standard API. Need some other methods to implement. - - da8xx_gpio.c - ------------ - Meets standard API. Implements gpio_request() properly. Simple conversion - possible. - - kw_gpio.c - --------- - Doesn't meet standard API. Needs some other methods to implement and move some - methods to another file. - - mpc83xx_gpio.c - -------------- - Meets standard API. Doesn't implement gpio_request() properly (only checks - if the pin is valid). Simple conversion possible. - - mvgpio.c - -------- - Meets standard API. Doesn't implement gpio_request() properly (only checks - if the pin is valid). Simple conversion possible. - - mvgpio.h - -------- - Wrong placement. Will be moved to another location. - - mvmfp.c - ------- - Wrong placement. Will be moved to another location. |