i2c: add init(pre-post) hooks

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

docs/platform-hooks.md

@@ -19,3 +19,6 @@ Any functionality perfomed here is done just before the normal function returns.
  * dir (replace-pre-post)
  * write (pre-post)
  * use-mmaped (replace-pre-post)
+
+### I2C
+ * init (pre-post) - On RAW

include/mraa_adv_func.h

@@ -46,4 +46,7 @@ typedef struct {
     mraa_result_t (*gpio_mmaped_write_replace) (mraa_gpio_context dev, int value);
     mraa_result_t (*gpio_mmaped_write_pre) (mraa_gpio_context dev, int value);
     mraa_result_t (*gpio_mmaped_write_post) (mraa_gpio_context dev, int value);
+
+    mraa_result_t (*i2c_init_pre) (unsigned int bus);
+    mraa_result_t (*i2c_init_post) (mraa_i2c_context dev);
 } mraa_adv_func_t;

src/i2c/i2c.c

@@ -50,6 +50,10 @@ mraa_i2c_init(int bus)
 mraa_i2c_context
 mraa_i2c_init_raw(unsigned int bus)
 {
+    if (advance_func->i2c_init_pre != NULL) {
+        if (advance_func->i2c_init_pre(bus) != MRAA_SUCCESS)
+            return NULL;
+    }
     mraa_i2c_context dev = (mraa_i2c_context) malloc(sizeof(struct _i2c));
     if (dev == NULL)
         return NULL;
@@ -59,6 +63,14 @@ mraa_i2c_init_raw(unsigned int bus)
     if ((dev->fh = open(filepath, O_RDWR)) < 1) {
         fprintf(stderr, "Failed to open requested i2c port %s\n", filepath);
     }
+
+    if (advance_func->i2c_init_post != NULL) {
+        mraa_result_t ret = advance_func->i2c_init_post(dev);
+        if (ret != MRAA_SUCCESS) {
+            free(dev);
+            return NULL;
+        }
+    }
     return dev;
 }