py: Fix mp_get_buffer, and use it in more places.

Must use mp_obj_get_type to get the type of an object.  Can't assume
mp_obj_t is castable to mp_obj_base_t.

py/obj.c

@@ -333,11 +333,11 @@ mp_obj_t mp_identity(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_identity_obj, mp_identity);
 
 bool mp_get_buffer(mp_obj_t obj, buffer_info_t *bufinfo) {
-    mp_obj_base_t *o = (mp_obj_base_t *)obj;
-    if (o->type->buffer_p.get_buffer == NULL) {
+    mp_obj_type_t *type = mp_obj_get_type(obj);
+    if (type->buffer_p.get_buffer == NULL) {
         return false;
     }
-    o->type->buffer_p.get_buffer(o, bufinfo, BUFFER_READ);
+    type->buffer_p.get_buffer(obj, bufinfo, BUFFER_READ);
     if (bufinfo->buf == NULL) {
         return false;
     }

py/objfun.c

@@ -442,14 +442,15 @@ STATIC machine_uint_t convert_obj_for_inline_asm(mp_obj_t obj) {
             mp_obj_t *items;
             mp_obj_list_get(obj, &len, &items);
             return (machine_uint_t)items;
-        } else if (type->buffer_p.get_buffer != NULL) {
-            // supports the buffer protocol, get a pointer to the data
-            buffer_info_t bufinfo;
-            type->buffer_p.get_buffer(obj, &bufinfo, BUFFER_READ);
-            return (machine_uint_t)bufinfo.buf;
         } else {
-            // just pass along a pointer to the object
-            return (machine_uint_t)obj;
+            buffer_info_t bufinfo;
+            if (mp_get_buffer(obj, &bufinfo)) {
+                // supports the buffer protocol, return a pointer to the data
+                return (machine_uint_t)bufinfo.buf;
+            } else {
+                // just pass along a pointer to the object
+                return (machine_uint_t)obj;
+            }
         }
     }
 }

stmhal/dac.c

@@ -180,12 +180,8 @@ mp_obj_t pyb_dac_dma(uint n_args, const mp_obj_t *args, mp_map_t *kw_args) {
     // set TIM6 to trigger the DAC at the given frequency
     TIM6_Config(mp_obj_get_int(args[2]));
 
-    mp_obj_type_t *type = mp_obj_get_type(args[1]);
-    if (type->buffer_p.get_buffer == NULL) {
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "buffer argument must support buffer protocol"));
-    }
     buffer_info_t bufinfo;
-    type->buffer_p.get_buffer(args[1], &bufinfo, BUFFER_READ);
+    mp_get_buffer_raise(args[1], &bufinfo);
 
     __DMA1_CLK_ENABLE();
 

stmhal/i2c.c

@@ -143,16 +143,13 @@ STATIC mp_obj_t pyb_i2c_mem_write(uint n_args, const mp_obj_t *args) {
     machine_uint_t i2c_addr = mp_obj_get_int(args[1]) << 1;
     machine_uint_t mem_addr = mp_obj_get_int(args[2]);
     HAL_StatusTypeDef status;
-    mp_obj_type_t *type = mp_obj_get_type(args[3]);
-    if (type->buffer_p.get_buffer != NULL) {
-        buffer_info_t bufinfo;
-        type->buffer_p.get_buffer(args[3], &bufinfo, BUFFER_READ);
-        status = HAL_I2C_Mem_Write(self->i2c_handle, i2c_addr, mem_addr, I2C_MEMADD_SIZE_8BIT, bufinfo.buf, bufinfo.len, 200);
-    } else if (MP_OBJ_IS_INT(args[3])) {
+    if (MP_OBJ_IS_INT(args[3])) {
         uint8_t data[1] = {mp_obj_get_int(args[3])};
         status = HAL_I2C_Mem_Write(self->i2c_handle, i2c_addr, mem_addr, I2C_MEMADD_SIZE_8BIT, data, 1, 200);
     } else {
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "data argument must be an integer or support the buffer protocol"));
+        buffer_info_t bufinfo;
+        mp_get_buffer_raise(args[3], &bufinfo);
+        status = HAL_I2C_Mem_Write(self->i2c_handle, i2c_addr, mem_addr, I2C_MEMADD_SIZE_8BIT, bufinfo.buf, bufinfo.len, 200);
     }
 
     //printf("Write got %d\n", status);