On Fri, Dec 02, 2016 at 07:33:46PM -0500, Jon Masters wrote: > On 12/02/2016 06:39 PM, Bjorn Helgaas wrote: > > On Thu, Dec 01, 2016 at 11:08:23PM -0500, Jon Masters wrote: > > >> Let's see if I summarized this correctly... > >> > >> 1. The MMIO registers for the host bridge itself need to be described > >> somewhere, especially if we need to find those in a quirk and poke > >> them. Since those registers are very much part of the bridge device, > >> it makes sense for them to be in the _CRS for PNP0A08/PNP0A03. > >> > >> 2. The address space covering these registers MUST be described as a > >> ResourceConsumer in order to avoid accidentally exposing them as > >> available for use by downstream devices on the PCI bus. > >> > >> 3. The ACPI specification allows for resources of the type "Memory32Fixed". > >> This is a macro that doesn't have the notion of a producer or consumer. > >> HOWEVER various interpretations seem to be that this could/should > >> default to being interpreted as a consumed region. > > > > I agree; I think that per spec, Memory24, Memory32, Memory32Fixed, IO, > > and FixedIO should all be for consumed resources, not for bridge > > windows, since they don't have the notion of producer. > > Ok. If we ultimately codify this somewhere as the general Linux kernel > consensus (Rafael?) then we can also go and get the various ARM server > specs updated to reflect this in (for e.g.) reference firmware builds. > > > I'm pretty sure there's x86 firmware in the field that uses these for > > windows, so I think we have to accept that usage, at least on x86. > > Ok. I was pondering how to even go about finding that out, but even if > I scheduled a job across RH's infra to look, that would be a drop in > the bucket of possible machines that might be out there doing this. Hmmm, when researching this, I thought I came across a change specifically for a machine that used Memory32Fixed this way, but I can't find it now. The only thing I did find was some old experiments with Windows that showed it interpreting a Memory32Fixed region as a window and putting PCI devices in it: https://bugzilla.kernel.org/show_bug.cgi?id=15817 But that was a synthetic example with qemu, not a real machine in the field. > > Even without this patch, I don't think it's a show-stopper to have > > Linux mistakenly thinking this region is routed to PCI, because the > > driver does reserve it and the PCI core will never try to use it. > > Ok. So are you happy with pulling in Duc's v4 patch and retaining > status quo on the bridge resources for 4.10? Yes, I think it looks good. I'll finish packaging things up and repost the current series. Bjorn -- 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
