Hi, Any progress on this one? I guess it won't make into 3.8, perhaps 3.9? On Friday 04 January 2013 00:44:16 Rafael J. Wysocki wrote: > On Thursday, January 03, 2013 04:00:55 PM Bjorn Helgaas wrote: > > On Thu, Jan 3, 2013 at 3:38 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > > 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. > > > > It's only a problem if you make the assumptions Linux does. I can > > imagine a system with different assumptions. For example, an OS could > > start with PCI device X and ask "please run any _PS0 method that > > matches X." In that case, you don't care how many objects have an > > _ADR that matches X; you merely find *any* matching object that > > contains _PS0. > > Well, except when there are multiple matching objects having _PS0. > Which actually happens in the failing case in bug #42696. > > Our assumptions work pretty well on other systems and I don't quite see the > reason to change them entirely. > > Moreover, Section 19.5.30 of the spec says that "Device object [...] > represents either a bus or a device or any other similar hardware". That > implies that if there are two objects with the same _ADR matching the same > single devfn of a PCI device, that will mean that there are _two_ different > PCI devices under the same parent that have the same devfn. In that case > PCI config space accesses wouldn't work for those devices, though. > > > >> 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? > > > > That's a good question. It's more complicated if two objects supply > > the same method. > > Well it is and they do. > > > >> 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. > > > > Is there something in the spec that says you can't? I can imagine a > > BIOS writer doing that, and I don't know how I could convince him that > > it's illegal. > > Well, OK. > > > It would be really interesting to try some of these scenarios on > > Windows with qemu. > > That's interesting theoretically, but doesn't directly relate to the case at > hand. The case at hand is that for a given PCI device we want to find the > ACPI namespace node that can be used for things like power management, if > one exists. While it may be valid to specify _ADR of type 0x0003ffff for > some namespace nodes, I don't really think it is valid to specify two > objects with the same _ADR matching a specific devfn that both provide the > same methods (like _PSx or _CRS). > > And the question we need to answer is not "I have a namespace node, so which > device it represents?", but "I have a device, so which namespace node > provides methods I'm supposed to use for it?" > > So I think we make the right assumptions, but there are broken BIOSes that > don't follow them and I'm trying to find out how to handle them without > blacklisting etc. > > Questioning the validity of everything we're doing doesn't really help, mind > you. > > Thanks, > Rafael Regards, Peter -- 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
