Hi, On Tue, Nov 29, 2016 at 7:43 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > Per spec, the Consumer/Producer bit is defined only for Extended > Address Space descriptors and should be ignored for QWord/DWord/Word > Address Space descriptors. My understanding is that this is because > x86 BIOSes didn't use the bit consistently, so it couldn't be relied > upon. The Extended descriptors were added later and are presumably > more reliable. > > Linux currently looks at Consumer/Producer for all Address Space > descriptors, although we don't use the result very much. The x86 and > ia64 host bridge driver code doesn't use Consumer/Producer to identify > windows; it assumes all descriptors are windows. > > We do currently use Consumer/Producer to decide whether to apply _TRA. > The change in these patches is to ignore Consumer/Producer for > QWord/DWord/Word, so we'll apply _TRA from Consumer descriptors where > we didn't before. Per spec, that should be safe because _TRA is > required to be zero for Consumer resources. > > If we want to describe host bridge register space and ECAM space > directly in the PNP0A03 device on ARM64 (and I guess potentially even > on x86 & ia64), I think we need changes like this so the arch code can > use IORESOURCE_WINDOW to tell which descriptors are windows and which > are registers. It would be good to copy/move the above paragraph to the changelog of patch [2/2]. The reason for that change is quite unclear otherwise. > This is a subtle area, so please take a look and let me know what you > think. > > These patches are based on v4.9-rc1. It's getting pretty late in the > cycle, but I think we'd really like to get the ARM64 ACPI PCI story > sorted out for the v4.10 merge window. So it is better if changes of this sort spend a few weeks in linux-next before they get merged, just in case they trigger some obscure issue and need to be rethought. I'm not against these changes, but I won't be entirely comfortable with them going straight into the mainline. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
