On 2015/6/12 8:28, Rafael J. Wysocki wrote: > On Thursday, June 11, 2015 12:41:29 PM Mika Westerberg wrote: >> On Thu, Jun 11, 2015 at 03:24:02AM +0200, Rafael J. Wysocki wrote: >>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >>> >>> Document how the ACPI device enumeration code uses the special >>> PRP0001 device ID. >>> >>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >> At last the long needed documentation regarding PRP0001 :-) Thank you >> for doing this, >> >> Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> >> >> One typo found, see below. > Thanks! > > I've fixed this one and added a clarification about enumerating I2C and SPI > clients with PRP0001 and "compatible". > > Updated patch is below. > > --- > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Subject: ACPI / enumeration: Document the rules regarding the PRP0001 device ID > > Document how the ACPI device enumeration code uses the special > PRP0001 device ID. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > --- > Documentation/acpi/enumeration.txt | 51 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > Index: linux-pm/Documentation/acpi/enumeration.txt > =================================================================== > --- linux-pm.orig/Documentation/acpi/enumeration.txt > +++ linux-pm/Documentation/acpi/enumeration.txt > @@ -359,3 +359,54 @@ the id should be set like: > The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under > the MFD device and if found, that ACPI companion device is bound to the > resulting child platform device. > + > +Device Tree namespace link device ID > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > +The Device Tree protocol uses device indentification 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 > +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 > +is only needed to indicate that a given device is compatible with another one, > +presumably having a matching driver in the kernel already. > + > +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 > +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. > + > +The special DT namespace link device ID, PRP0001, provides a means to use the > +existing DT-compatible device identification in ACPI and to satisfy the above > +requirements following from the ACPI specification at the same time. Namely, > +if PRP0001 is returned by _HID, the ACPI subsystem will look for the > +"compatible" property in the device object's _DSD and will use the value of that > +property to identify the corresponding device in analogy with the original DT > +device identification algorithm. If the "compatible" property is not present > +or its value is not valid, the device will not be enumerated by the ACPI > +subsystem. Otherwise, it will be enumerated automatically as a platform device > +(except when an I2C or SPI link from the device to its parent is present, in > +which case the ACPI core will leave the device enumeration to the parent's > +driver) and the identification strings from the "compatible" property value will > +be used to find a driver for the device along with the device IDs listed by _CID > +(if present). > + > +Analogously, if PRP0001 is present in the list of device IDs returned by _CID, > +the identification strings listed by the "compatible" property value (if present > +and valid) will be used to look for a driver matching the device, but in that > +case their relative priority with respect to the other device IDs listed by > +_HID and _CID depends on the position of PRP0001 in the _CID return package. > +Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID > +return package will be checked first. Also in that case the bus type the device > +will be enumerated to depends on the device ID returned by _HID. > + > +It is valid to define device objects with a _HID returning PRP0001 and without > +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. > Thanks for documenting this, it's very useful :) Reviewed-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx> Thanks Hanjun -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
