On Friday 22 June 2012, Thierry Reding wrote: > On Fri, Jun 22, 2012 at 05:46:52AM -0600, Bjorn Helgaas wrote: > > On Fri, Jun 22, 2012 at 5:00 AM, Thierry Reding > > <thierry.reding@xxxxxxxxxxxxxxxxx> wrote: > > >> Is the bus number aperture included somewhere? How do we know what > > >> bus numbers are available for allocation under each bridge? > > > > > > Not yet. I don't think DT imposes a bus number allocation on PCI > > > bridges. However the matching of DT nodes to PCI bridges is done based > > > on the bus number. For that you provide a bus-ranges property which > > > defines the bus aperture of the given PCI bridge. The DT matching code > > > compares the first cell of this property with the primary bus number of > > > the bridge. > > > > I don't fully understand this, but I can tell you that things don't > > work very well if we don't know the aperture. We can make > > assumptions, like the root bus is 00, and then enumerate everything > > reachable from there. But then all we know is the largest bus number > > actually reachable from bus 00, which is usually smaller then the end > > of the aperture. We don't know how many unused bus numbers there are > > in the aperture, so we can't safely allocate any for hot-added > > devices. I believe the assumption today is that all bus numbers are ok on each root port, which is usually the case. There was something about a Power Mac that faked a single PCI bus number space across both an AGP and a PCIe domain in pmac_pci_fixup_u4_of_node(), but I think that is the exception. Is there any requirement to use a bus aperture on non-PC hardware? > I think DT support for PCI is lacking in a lot of areas. PowerPC seems > to be the only architecture actively setting up busses according to the > bus-range property specified in the DT. All other architectures seem to > not pre-allocate bus apertures and go with the default instead. From > what you say that means hot-plugging is out. Although I don't think the > Tegra PCIe controller even supports hot-plugging. If the default is allowing any bus numbers, and that matches the hardware capabilities, I think hot-plugging would work. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
