diff options
Diffstat (limited to 'Documentation/acpi/enumeration.txt')
| -rw-r--r-- | Documentation/acpi/enumeration.txt | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt index a91ec5af52df..7bcf9c3d9fbe 100644 --- a/Documentation/acpi/enumeration.txt +++ b/Documentation/acpi/enumeration.txt @@ -367,10 +367,10 @@ resulting child platform device. Device Tree namespace link device ID ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The Device Tree protocol uses device indentification based on the "compatible" +The Device Tree protocol uses device identification based on the "compatible" property whose value is a string or an array of strings recognized as device identifiers by drivers and the driver core. The set of all those strings may be -regarded as a device indentification namespace analogous to the ACPI/PNP device +regarded as a device identification namespace analogous to the ACPI/PNP device ID namespace. Consequently, in principle it should not be necessary to allocate a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing identification string in the Device Tree (DT) namespace, especially if that ID @@ -381,7 +381,7 @@ In ACPI, the device identification object called _CID (Compatible ID) is used to list the IDs of devices the given one is compatible with, but those IDs must belong to one of the namespaces prescribed by the ACPI specification (see Section 6.1.2 of ACPI 6.0 for details) and the DT namespace is not one of them. -Moreover, the specification mandates that either a _HID or an _ADR identificaion +Moreover, the specification mandates that either a _HID or an _ADR identification object be present for all ACPI objects representing devices (Section 6.1 of ACPI 6.0). For non-enumerable bus types that object must be _HID and its value must be a device ID from one of the namespaces prescribed by the specification too. @@ -415,3 +415,12 @@ the "compatible" property in the _DSD or a _CID as long as one of their ancestors provides a _DSD with a valid "compatible" property. Such device objects are then simply regarded as additional "blocks" providing hierarchical configuration information to the driver of the composite ancestor device. + +However, PRP0001 can only be returned from either _HID or _CID of a device +object if all of the properties returned by the _DSD associated with it (either +the _DSD of the device object itself or the _DSD of its ancestor in the +"composite device" case described above) can be used in the ACPI environment. +Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible" +property returned by it is meaningless. + +Refer to DSD-properties-rules.txt for more information. |