Hi Everyone, This has been in the works for some time, but the official document it is based on was not quite ready before the last week. It now is available at http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.pdf The issue at hand is that we need to be able to support hierarchical device properties in ACPI, like when the set of properties of an entity called "Fred" may include a subset called "dog" containing the properties of the Fred's dog rather than those of Fred himself. And it may make sense to have the same property, like "hair color", for both Fred and the dog, but with different values. We (I, Darren and Dave at least) have explored many possible ways to deal with that in ACPI, but the majority of them turned out to be unattractive for various reasons. Our first take was to use ACPI device objects to make the "child" property sets available via _DSD, but that approach is generally incompatible with the PnP Manager in Windows following the notion that all device objects in ACPI tables are supposed to represent real devices. It can still be made work by adding _STA that returns 0 to those "property-only" device objects, but that leads to complications in other places and is error prone (if the _STA is forgotten, for example). Moreover, it adds quite a bit of overhead even in Linux (an ACPICA representation, struct acpi_device, driver core mechanics etc) for things that are only supposed to represent sets of device properties. And, in addition to that, we'd need to figure out how to give those things arbitrary names in a consistent way. All of that caused us to drop the approach based on device objects and look for other options. One of those was to nest the "child" property sets within _DSD packages, but it follows from experience that this is error prone too (firmware people tend to have problems with getting deeply nested packages right in ASL) and we wanted to be able to visually distinguish those sets as separate entities in ASL code. That led us to the directory concept defined by the document mentioned above. The idea is that _DSD may return a package containing the properties of the device it belongs to along with a directory of objects that need to be evaluated in order to obtain the "child" property sets of it. That directory needs to be present in a separate section of the _DSD package (after the new UUID defined in the above document) and is a list of two-element sub-packages (entries) where the first element is the name of the entry (the name of the "child" property set represented by it) and the second element is a "pointer" (essentially, a path or "namestring" in the ACPI terminology) to the control method or a static data package that needs to be evaluated to obtain the entry's data. The data returned by it is then interpreted in the same way as a _DSD return package, so it may also contain properties and a directory of its own "child" property sets. As an example, consider the following ASL from an experimental MinnowBoard firmware: Device (LEDS) { Name (_HID, "PRP0001") Name (_CRS, ResourceTemplate () { GpioIo (Exclusive, PullDown, 0, 0, IoRestrictionOutputOnly, "\\_SB.PCI0.LPC", 0, ResourceConsumer) {10} GpioIo (Exclusive, PullDown, 0, 0, IoRestrictionOutputOnly, "\\_SB.PCI0.LPC", 0, ResourceConsumer) {11} }) Name (_DSD, Package () { ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), Package () { Package () {"compatible", Package () {"gpio-leds"}}, }, // Data extension ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), Package () { Package () {"heartbeat", "LEDH"}, Package () {"mmc-activity", "LEDM"}, } }) Name (LEDH, Package () { ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), Package () { Package () {"label", "Heartbeat"}, Package () {"gpios", Package () {^LEDS, 0, 0, 0}}, Package () {"linux,default-trigger", "heartbeat"}, Package () {"linux,default-state", "off"}, Package () {"linux,retain-state-suspended", 1}, } }) Name (LEDM, Package () { ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), Package () { Package () {"label", Package () {"MMC0 Activity"}}, Package () {"gpios", Package () {^LEDS, 1, 0, 0}}, Package () {"linux,default-trigger", Package () {"mmc0"}}, Package () {"linux,default-state", "off"}, Package () {"linux,retain-state-suspended", 1}, } }) } where each LED in a GPIO LED array is represented by a "child" property set of the master device object LEDS. There are two "child" sets called "heartbeat" and "mmc-activity" whose data come from the LEDH and LEDM static data packages under LEDS, respectively. The patch series introduces an infrastructure allowing "child" property sets like the above to be accessed via the generic device properties API. It represents those property sets as structures extending struct fwnode_handle with the new type FWNODE_ACPI_DATA and reworks the ACPI property handling code to do the right thing if an fwnode_handle of that type is passed to it (please refer to the patch changelogs for details). Please note that this new mechanism is not a replacement for anything. It simply adds general support for representing hierarchical properties of devices in a new way, but things that worked previously should still work. Also please let me know if you have objections agaist this approach or suggestions on improving the code. Although the 4.3 merge window has not officially opened yet, I'm not regarding this as 4.3 material unless someone wants it in 4.3 really badly, in which case please let me know ASAP as well. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html