On Wed, Aug 15, 2012 at 07:36:24AM -0700, Bjorn Helgaas wrote: > On Wed, Aug 15, 2012 at 5:30 AM, Thierry Reding > <thierry.reding@xxxxxxxxxxxxxxxxx> wrote: > > On Wed, Aug 15, 2012 at 05:18:04AM -0700, Bjorn Helgaas wrote: > >> On Tue, Aug 14, 2012 at 11:37 PM, Thierry Reding > >> <thierry.reding@xxxxxxxxxxxxxxxxx> wrote: > >> > On Tue, Aug 14, 2012 at 04:50:26PM -0700, Bjorn Helgaas wrote: > >> >> On Tue, Aug 14, 2012 at 1:12 PM, Thierry Reding > >> >> <thierry.reding@xxxxxxxxxxxxxxxxx> wrote: > >> >> > On Thu, Jul 26, 2012 at 09:55:12PM +0200, Thierry Reding wrote: > >> >> >> diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi > >> >> >> index a094c97..c886dff 100644 > >> >> >> --- a/arch/arm/boot/dts/tegra20.dtsi > >> >> >> +++ b/arch/arm/boot/dts/tegra20.dtsi > >> >> >> @@ -199,6 +199,68 @@ > >> >> >> #size-cells = <0>; > >> >> >> }; > >> >> >> > >> >> >> + pcie-controller { > >> >> >> + compatible = "nvidia,tegra20-pcie"; > >> >> >> + reg = <0x80003000 0x00000800 /* PADS registers */ > >> >> >> + 0x80003800 0x00000200 /* AFI registers */ > >> >> >> + 0x81000000 0x01000000 /* configuration space */ > >> >> >> + 0x90000000 0x10000000>; /* extended configuration space */ > >> >> >> + interrupts = <0 98 0x04 /* controller interrupt */ > >> >> >> + 0 99 0x04>; /* MSI interrupt */ > >> >> >> + status = "disabled"; > >> >> >> + > >> >> >> + ranges = <0 0 0 0x80000000 0x00001000 /* root port 0 */ > >> >> >> + 0 1 0 0x81000000 0x00800000 /* port 0 config space */ > >> >> >> + 0 2 0 0x90000000 0x08000000 /* port 0 ext config space */ > >> >> >> + 0 3 0 0x82000000 0x00010000 /* port 0 downstream I/O */ > >> >> >> + 0 4 0 0xa0000000 0x08000000 /* port 0 non-prefetchable memory */ > >> >> >> + 0 5 0 0xb0000000 0x08000000 /* port 0 prefetchable memory */ > >> >> >> + > >> >> >> + 1 0 0 0x80001000 0x00001000 /* root port 1 */ > >> >> >> + 1 1 0 0x81800000 0x00800000 /* port 1 config space */ > >> >> >> + 1 2 0 0x98000000 0x08000000 /* port 1 ext config space */ > >> >> >> + 1 3 0 0x82010000 0x00010000 /* port 1 downstream I/O */ > >> >> >> + 1 4 0 0xa8000000 0x08000000 /* port 1 non-prefetchable memory */ > >> >> >> + 1 5 0 0xb8000000 0x08000000>; /* port 1 prefetchable memory */ > >> >> > > >> >> > I've been thinking about this some more. The translations for both the > >> >> > regular and extended configuration spaces are configured in the top- > >> >> > level PCIe controller. It is therefore wrong how they are passed to the > >> >> > PCI host bridges via the ranges property. > >> >> > > >> >> > I remember Mitch saying that it should be passed down to the children > >> >> > because it is partitioned among them, but since the layout is compatible > >> >> > with ECAM, the partitioning isn't as simple as what's in the tree. In > >> >> > fact the partitions will be dependent on the number of devices attached > >> >> > to the host bridges. > >> >> > >> >> I don't understand this last bit about the number of devices attached > >> >> to the host bridges. Logically, the host bridge has a bus number > >> >> aperture that you can know up front, even before you know anything > >> >> about what devices are below it. On x86, for example, the ACPI _CRS > >> >> method has something like "[bus 00-7f]" in it, which means that any > >> >> buses in that range are below this bridge. That doesn't tell us > >> >> anything about which buses actually have devices on them, of course; > >> >> it's just analogous to the secondary and subordinate bus number > >> >> registers in a P2P bridge. > >> > > >> > That's one of the issues I still need to take care of. Currently no bus > >> > resource is attached to the individual bridges (nor the PCI controller > >> > for that matter), so the PCI core will assign them dynamically. > >> > >> So your PCI controller driver knows how to program the controller bus > >> number aperture? Sometimes people start by assuming that two host > >> bridges both have [bus 00-ff] apertures, then they enumerate below the > >> first and adjust the bus number apertures based on what they found. > >> For example, if they found buses 00-12 behind the first bridge, they > >> make the apertures [bus 00-12] for the first bridge and [bus 13-ff] > >> for the second. That might be the case, depending on what firmware > >> set up, but it seems like a dubious way to do it, and of course it > >> precludes a lot of hot-plug scenarios. > > > > No, that's not what I meant. What happens is that no pre-assigned bus > > range is specified for either of the host bridges, so that the range > > 0x00-0xff will be assigned by default in pci_scan_root_bus(). > > My concern is about making the kernel's idea of the host bridge bus > number aperture match what the hardware is doing. I'm pretty sure > that the default [bus 00-ff] range assigned by pci_scan_root_bus() > doesn't actually match the hardware in most cases, at least when we > have multiple host bridges in the same PCI domain. > > For example, if you don't supply a bus number range, > pci_scan_root_bus() will assume [bus 00-ff] for both host bridges. > But if you could put an analyzer on each of the root buses and then > read bus 0 config space, will you see that config transaction on > *both* buses? I doubt it. > > You have to know at least the bus number of the root bus up front > before you can even start enumerating it. The only way to learn that > is by reading registers in the host bridge or by some external > mechanism like ACPI or device tree. That's the beginning of the bus > number aperture. The end of the aperture is similar: we can't > reliably determine it by enumerating devices below the host bridge, so > we have to know it up front. You can enumerate starting with the root > bus number and assigning new subordinate bus numbers as necessary, but > unless you know the host bridge aperture to begin with, you could > inadvertently assign a new bus number that actually belongs to a > different host bridge. Yes, that was my understanding as well. So currently I haven't seen any problems with this because I only use one of the two host bridges. But I suppose I should add code to initialize the bus number aperture properly either via platform device resources (for the non-DT case) and the device tree otherwise. Thierry
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