内核ACPI函数API之acpi_get

acpi_get_devices(const char *HID, acpi_walk_callback user_function,   void *context, void **return_value) 根据形参指定的参数返回一个acpi_device，其中的HID 可能为null
其源码分析如下：acpi_status
acpi_get_devices(const char *HID,acpi_walk_callback user_function,void *context, void **return_value)
{acpi_status status;struct acpi_get_devices_info info;ACPI_FUNCTION_TRACE(acpi_get_devices);/* Parameter validation */#可以看到形参hid可以为null，但是user_function 不能为nullif (!user_function) {return_ACPI_STATUS(AE_BAD_PARAMETER);}/** We're going to call their callback from OUR callback, so we need* to know what it is, and their context parameter.*/#用形参给info赋值info.hid = HID;info.context = context;info.user_function = user_function;/** Lock the namespace around the walk.* The namespace will be unlocked/locked around each call* to the user function - since this function* must be allowed to make Acpi calls itself.*/status = acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);if (ACPI_FAILURE(status)) {return_ACPI_STATUS(status);}#开始从root 遍历所有类型为device的设备，来匹配info中的信息以寻找对应的acpi_device，结果保存在return_value中返回status = acpi_ns_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,ACPI_UINT32_MAX, ACPI_NS_WALK_UNLOCK,acpi_ns_get_device_callback, NULL,&info, return_value);(void)acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);return_ACPI_STATUS(status);
}我们继续看看acpi_ns_walk_namespace 中为查找acpi_device所有的callback函数
static acpi_status
acpi_ns_get_device_callback(acpi_handle obj_handle,u32 nesting_level,void *context, void **return_value)
{struct acpi_get_devices_info *info = context;acpi_status status;struct acpi_namespace_node *node;u32 flags;struct acpi_pnp_device_id *hid;struct acpi_pnp_device_id_list *cid;u32 i;u8 found;int no_match;status = acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);if (ACPI_FAILURE(status)) {return (status);}#检查handle是否有效node = acpi_ns_validate_handle(obj_handle);status = acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);if (ACPI_FAILURE(status)) {return (status);}if (!node) {return (AE_BAD_PARAMETER);}#search acpi_device分为两种情况，首先查找HID,如果没有查找到HID或者HID 为null，则开始执行user function查找if (info->hid != NULL) {#得到node的hidstatus = acpi_ut_execute_HID(node, &hid);if (status == AE_NOT_FOUND) {return (AE_OK);} else if (ACPI_FAILURE(status)) {return (AE_CTRL_DEPTH);}#hid就是一个字符串，这里通过strcmp比较字符串是否相等no_match = strcmp(hid->string, info->hid);ACPI_FREE(hid);#如果hid没有找到，则继续找cid，从for循环可以看出一个hid可以对应多个cidif (no_match) {/** HID does not match, attempt match within the* list of Compatible IDs (CIDs)*/status = acpi_ut_execute_CID(node, &cid);if (status == AE_NOT_FOUND) {return (AE_OK);} else if (ACPI_FAILURE(status)) {return (AE_CTRL_DEPTH);}/* Walk the CID list */#遍历所有的cidfound = FALSE;for (i = 0; i < cid->count; i++) {if (strcmp(cid->ids[i].string, info->hid) == 0) {/* Found a matching CID */found = TRUE;break;}}ACPI_FREE(cid);if (!found) {return (AE_OK);}}}/* Run _STA to determine if device is present */#如果hid和cid 都没有匹配，则执行STA 来判断这个device是否存在status = acpi_ut_execute_STA(node, &flags);if (ACPI_FAILURE(status)) {return (AE_CTRL_DEPTH);}if (!(flags & ACPI_STA_DEVICE_PRESENT) &&!(flags & ACPI_STA_DEVICE_FUNCTIONING)) {/** Don't examine the children of the device only when the* device is neither present nor functional. See ACPI spec,* description of _STA for more information.*/return (AE_CTRL_DEPTH);}/* We have a valid device, invoke the user function */#hid和cid 都没有匹配，而且STA返回ok的话，则执行用户指定的user_function来继续查找acpi_devicestatus = info->user_function(obj_handle, nesting_level,info->context, return_value);return (status);
}

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