On Wed, May 30, 2012 at 1:40 AM, Steven Newbury <steve@xxxxxxxxxxxxxxx> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 30/05/12 00:27, Bjorn Helgaas wrote: >> On Tue, May 29, 2012 at 2:40 PM, Yinghai Lu <yinghai@xxxxxxxxxx> >> wrote: >>> On Tue, May 29, 2012 at 12:23 PM, Bjorn Helgaas >>> <bhelgaas@xxxxxxxxxx> wrote: >>>> On Tue, May 29, 2012 at 12:17 PM, Yinghai Lu >>>> <yinghai@xxxxxxxxxx> wrote: >>>>> On Tue, May 29, 2012 at 10:57 AM, H. Peter Anvin >>>>> <hpa@xxxxxxxxx> wrote: >>>>>> On 05/29/2012 10:55 AM, Yinghai Lu wrote: > > *SNIP* > >>> >>> >>> ok, please check the version, that put back PCI_MAX_RESOURCE_32 >>> for io ports. >>> >>> also RFC to limit for 16 bit ioport handling. only help other >>> arches that does support 32bit ioports but have bridges only >>> support 16bit io ports. >> >> I don't understand this one at all. It looks like you mashed >> together at least two changes: (1) prefer I/O space above 64K if >> available, and (2) mark secondary bus resources with >> IORESOURCE_IO_32 when the P2P bridge I/O window address decode type >> is PCI_IO_RANGE_TYPE_32 and use that to limit allocations. >> >> I don't see the justification for (1). What problem does this >> solve? >> > I can potentially see this helping with hotplug, where a new device > has only 16 bit io ports, but if there's no space remaining under 64k > allocation would fail. Preferring above 64k means preserving that > limited resource. This is exactly equivalent to my original > motivation for preferring 64 bit PCI mem in order to preserve 32 bit > address space for hotplug devices without 64 bit BARs. You're right, the spec does allow the upper 16 bits of I/O BARs to be hardwired to zero (PCI spec rev 3.0, p. 226), so this part does make some sense. I don't think it applies to x86, since I don't think there's a way to generate an I/O access to anything above 64K, but it could help other arches. I'm inclined to be conservative and wait until we find a problem where a patch like this would help. -- 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
