On Thursday, January 03, 2013 02:44:32 PM Bjorn Helgaas wrote: > On Thu, Jan 3, 2013 at 1:17 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Thursday, January 03, 2013 08:16:26 AM Bjorn Helgaas wrote: > >> On Fri, Dec 28, 2012 at 2:29 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > >> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > >> > > >> > As the kernel Bugzilla report #42696 indicates, it generally is not > >> > sufficient to use _ADR to get an ACPI device node corresponding to > >> > the given PCI device, because there may be multiple objects with > >> > matching _ADR in the ACPI namespace (this probably is against the > >> > spec, but it evidently happens in practice). > >> > >> I don't see anything in sec 6.1.1 (_ADR) that precludes having > >> multiple objects that contain the same _ADR. Do you have any other > >> pointers? > > > > Section 6.1 implicitly means that. It says that for PCI devices _ADR > > must be present to identify which device is represented by the given > > ACPI node. Next, Section 6.1.1 says that the parent bus should be inferred > > from the location of the _ADR object's device package in the ACPI namespace, > > so clearly, if that's under the PCI root bridge ACPI node, the _ADR > > corresponds to a PCI device's bus address. > > I agree that for namespace Devices below a PCI host bridge, the _ADR > value and its position in the hierarchy is required to be sufficient > to identify a PCI device and function (or the set of all functions on > a device #). > > > Then, Table 6-139 specifies the format of _ADR for PCI devices as being > > euqivalent to devfn, which means that if two nodes with the same _ADR are > > present in one scope (under one parent), then it is impossible to distinguish > > between them and that's against Section 6.1. > > This is the bit I don't understand. Where's the requirement that we > be able to distinguish between two namespace nodes with the same _ADR? According to the spec we can't (if they are under the same parent) and that's the whole problem. > Linux assumes we can start from a PCI device and identify a single > related ACPI namespace node, e.g., in acpi_pci_find_device(). But all > I see in the spec is a requirement that we can start from an ACPI > namespace node and find a PCI device. So I'm not sure > acpi_pci_find_device() is based on a valid assumption. I think it is. Suppose that we have two namespace nodes with the same _ADR under one parent (PCI bridge ACPI node) and they both contain things like _PS0 and _PS3. Which one of these are we supposed to use for the power management of the corresponding PCI device? Because they both would point to the same device, right? > Let's say we want to provide _SUN and _UID. _SUN is a slot number > that may apply to several PCI functions, while _UID probably refers to > a single PCI function. Is it legal to provide two namespace objects, > one with _ADR 0x0003ffff and _SUN, and another with _ADR 0x00030000 > and _UID? I don't think it is valid to do that. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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
