| Viktor Křivák | 25ee150 | 2012-08-08 13:42:19 +0200 | [diff] [blame] | 1 | The U-Boot Driver Model Project |
| 2 | =============================== |
| 3 | GPIO analysis |
| 4 | ============= |
| 5 | Viktor Krivak <viktor.krivak@gmail.com> |
| 6 | 2012-02-24 |
| 7 | |
| 8 | I) Overview |
| 9 | ----------- |
| 10 | |
| 11 | At this moment U-Boot provides standard API that consists of 7 functions. |
| 12 | |
| 13 | int gpio_request(unsigned gpio, const char *label) |
| 14 | int gpio_free(unsigned gpio) |
| 15 | int gpio_direction_input(unsigned gpio) |
| 16 | int gpio_direction_output(unsigned gpio, int value) |
| 17 | int gpio_get_value(unsigned gpio) |
| 18 | void gpio_set_value(unsigned gpio, int value) |
| 19 | |
| 20 | Methods "gpio_request()" and "gpio_free()" are used for claiming and releasing |
| 21 | GPIOs. First one should check if the desired pin exists and if the pin wasn't |
| 22 | requested already elsewhere. The method also has a label argument that can be |
| 23 | used for debug purposes. The label argument should be copied into the internal |
| 24 | memory, but only if the DEBUG macro is set. The "gpio_free()" is the exact |
| 25 | opposite. It releases the particular pin. Other methods are used for setting |
| 26 | input or output direction and obtaining or setting values of the pins. |
| 27 | |
| 28 | II) Approach |
| 29 | ------------ |
| 30 | |
| 31 | 1) Request and free GPIO |
| 32 | ------------------------ |
| 33 | |
| 34 | The "gpio_request()" implementation is basically the same for all boards. |
| 35 | The function checks if the particular GPIO is correct and checks if the |
| 36 | GPIO pin is still free. If the conditions are met, the method marks the |
| 37 | GPIO claimed in it's internal structure. If macro DEBUG is defined, the |
| 38 | function also copies the label argument to the structure. If the pin is |
| 39 | already locked, the function returns -1 and if DEBUG is defined, certain |
| 40 | debug output is generated, including the contents of the label argument. |
| 41 | The "gpio_free()" function releases the lock and eventually deallocates |
| 42 | data used by the copied label argument. |
| 43 | |
| 44 | 2) Internal data |
| 45 | ---------------- |
| 46 | |
| 47 | Internal data are driver specific. They have to contain some mechanism to |
| 48 | realise the locking though. This can be done for example using a bit field. |
| 49 | |
| 50 | 3) Operations provided by the driver |
| 51 | ------------------------------------ |
| 52 | |
| 53 | The driver operations basically meet API that is already defined and used. |
| 54 | Except for "gpio_request()" and "gpio_free()", all methods can be converted in |
| 55 | a simple manner. The driver provides the following structure: |
| 56 | |
| 57 | struct gpio_driver_ops { |
| 58 | int (*gpio_request)(struct instance *i, unsigned gpio, |
| 59 | const char *label); |
| 60 | int (*gpio_free)(struct instance *i, unsigned gpio); |
| 61 | int (*gpio_direction_input)(struct instance *i, unsigned gpio); |
| 62 | int (*gpio_direction_output)(struct instance *i, unsigned gpio, |
| 63 | int value); |
| 64 | int (*gpio_get_value)(struct instance *i, unsigned gpio); |
| 65 | void (*gpio_set_value)(struct instance *i, unsigned gpio, int value); |
| 66 | } |
| 67 | |
| 68 | III) Analysis of in-tree drivers |
| 69 | -------------------------------- |
| 70 | |
| 71 | 1) altera_pio.c |
| 72 | --------------- |
| 73 | Meets standard API. Implements gpio_request() properly. Simple conversion |
| 74 | possible. |
| 75 | |
| 76 | 2) at91_gpio.c |
| 77 | -------------- |
| 78 | Don't meet standard API. Need some other methods to implement. |
| 79 | |
| 80 | 3) da8xx_gpio.c |
| 81 | --------------- |
| 82 | Meets standard API. Implements gpio_request() properly. Simple conversion |
| 83 | possible. |
| 84 | |
| 85 | 4) kw_gpio.c |
| 86 | ------------ |
| 87 | Doesn't meet standard API. Needs some other methods to implement and move some |
| 88 | methods to another file. |
| 89 | |
| 90 | 5) mpc83xx_gpio.c |
| 91 | ----------------- |
| 92 | Meets standard API. Doesn't implement gpio_request() properly (only checks |
| 93 | if the pin is valid). Simple conversion possible. |
| 94 | |
| 95 | 6) mvgpio.c |
| 96 | ----------- |
| 97 | Meets standard API. Doesn't implement gpio_request() properly (only checks |
| 98 | if the pin is valid). Simple conversion possible. |
| 99 | |
| 100 | 7) mvgpio.h |
| 101 | ----------- |
| 102 | Wrong placement. Will be moved to another location. |
| 103 | |
| 104 | 8) mvmfp.c |
| 105 | ---------- |
| 106 | Wrong placement. Will be moved to another location. |