On Monday, April 13, 2015 12:31:20 PM Jiang Liu wrote: > On 2015/4/10 8:28, Rafael J. Wysocki wrote: > > On Fri, Apr 10, 2015 at 12:37 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > >> On Thursday, April 09, 2015 05:00:08 PM Bjorn Helgaas wrote: > >>> On Thu, Apr 9, 2015 at 4:37 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > >>>> On Thursday, April 09, 2015 10:50:02 AM Jiang Liu wrote: > >>>>> On 2015/4/9 7:44, Rafael J. Wysocki wrote: > >>>>>> On Wednesday, April 08, 2015 01:48:46 PM Jiang Liu wrote: > >>>>>>> On 2015/4/7 8:28, Rafael J. Wysocki wrote: > >>>>>>>> On Friday, April 03, 2015 10:04:11 PM Bjorn Helgaas wrote: > >>>>>>>>> Hi Jiang, > >>>>>>> <snip> > >>>>>>>>>> Currently acpi_dev_filter_resource_type() is only used by ACPI pci > >>>>>>>>>> host bridge and IOAPIC driver, so it shouldn't affect other drivers. > >>>>>>>>> > >>>>>>>>> We should assume it will eventually be used for all ACPI devices, > >>>>>>>>> shouldn't we? > >>>>>>>> > >>>>>>>> I'm not sure about that, really. In fact, I'd restrict its use to devices > >>>>>>>> types that actually can "produce" resources (ie. do not require the resources > >>>>>>>> to be provided by their ancestors or to be available from a global pool). > >>>>>>>> > >>>>>>>> Otherwise we're pretty much guaranteed to get into trouble. > >>>>>>>> > >>>>>>>> And all of the above rules need to be documented in the kernel source tree > >>>>>>>> or people will get confused. > >>>>>>> Hi Rafael, > >>>>>>> How about following comments for acpi_dev_filter_resource_type()? > >>>>>>> Thanks! > >>>>>>> Gerry > >>>>>>> -------------------------------------------------------------------- > >>>>>>> /** > >>>>>>> * According to ACPI specifications, Consumer/Producer flag in ACPI resource > >>>>>>> * descriptor means: > >>>>>>> * 1(CONSUMER): This device consumes this resource > >>>>>>> * 0(PRODUCER): This device produces and consumes this resource > >>>>>>> * But for ACPI PCI host bridge, it is interpreted in another way: > >>>>>> > >>>>>> So first of all, this leads to a question: Why is it interpreted for ACPI PCI > >>>>>> host bridges differently? > >>>>>> > >>>>>> Is it something we've figured out from experience, or is there a standard > >>>>>> mandating that? > >>>>> Hi Rafael, > >>>>> I think we got this knowledge by experiences. PCI FW spec only > >>>>> states _CRS reports resources assigned to the host bridge by firmware. > >>>>> There's no statement about whether the resource is consumed by host > >>>>> bridge itself or provided to it's child bus/devices. On x86/IA64 side, > >>>>> the main resource consumed by PCI host bridge is IOPORT 0xCF8-0xCFF, > >>>>> but not sure about ARM64 side. So how about: > >>>> > >>>> This: > >>>> > >>>>> PCI Firmware specification states that _CRS reports resources > >>>>> assigned to the host bridge, but there's no way to tell whether > >>>>> the resource is consumed by host bridge itself or provided to > >>>>> its child bus/devices. > >>>> > >>>> looks OK to me, but I'd replace the below with something like: > >>>> > >>>> "However, experience shows, that in the PCI host bridge case firmware writers > >>>> expect the resource to be provided to devices on the bus (below the bridge) for > >>>> consumption entirely if its Consumer/Producer flag is clear. That expectation > >>>> is reflected by the code in this routine as follows:". > >>> > >>> What a mess. The spec is regrettably lacking in Consumer/Producer > >>> specifics. But I don't see what's confusing about the descriptors > >>> that have Consumer/Producer bits. > >>> > >>> QWord, DWord, and Word descriptors don't seem to have a > >>> Consumer/Producer bit, but they do contain _TRA, so they must be > >>> intended for bridge windows. Can they also be used for device > >>> registers? I don't know. > >>> > >>> The Extended Address descriptor has a Consumer/Producer bit, and I > >>> would interpret the spec to mean that if the flag is clear (the device > >>> produces and consumes this resource), the resource is available on the > >>> bus below the bridge, i.e., the bridge consumes the resource on its > >>> upstream side and produces it on its downstream side. > >> > >> OK, that makes sense for bridges. > > >>> If the bit were > >>> set (the device only consumes the resource), I would expect that to > >>> mean the descriptor is for bridge registers like 0xcf8/0xcfc that > >>> never appear on the downstream side. > >> > >> That part is clear. What is not clear is whether or not we can *always* > >> expect the resources with Consumer/Producer *clear* to be produced on the > >> downstram side. That appears to be the case for host bridges if my > >> understanding of things is correct, but is it the case in general? > >> > >>> Maybe I'm reading the spec too naively, but this doesn't seem a matter > >>> of experience. > >> > >> Well, the specification is not clear enough in that respect, at least as > >> far as I can say, or maybe it is, but then does firmware always follow that > >> interpretation? > > > > So I guess I'd like to propose to go back to the 3.19 behavior for PCI host > > bridges and then to handle the IOAPIC as a separate case. > > > > We can think about consolidating the two later. > > > > Any objections to doing that? > Hi Rafael, > When reverting to the behavior before v3.19, I found a simpler > solution. The logic before v3.19 is: > on x86 and IA64, all IO port and MMIO resources assigned to PCI host > bridge are available to child bus/devices, except one special case to > filter out IO port[0xCF8-0xCFF] for PCI configuration space access. > > And with pre-v3.19 kernels, all IO port defined by IO and fixed_IO > resource descriptors are ignored to filter out IO port[0xCF8-0xCFF]. > > So I plan to make following change to revert to the behavior before > v3.19: > 1) make acpi_dev_filter_resource_type() filter descriptors based on > descriptor type, and don't check consumer_producer flag anymore. > 2) use IORESOURCE_IO_FIXED flag to filter out io and fixed_io resource > descriptors. > 3) x86 ACPI pci host bridge driver calls acpi_dev_filter_resource_type() > with flag IORESOURCE_IO_FIXED, > > By this way, we could keep acpi_dev_filter_resource_type() > as a generic interface and could be reused. And the change > is small too. Any comments? Sounds good to me. -- 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
