On Thu, Apr 11, 2024 at 08:13:18AM +0200, Sergio Paracuellos wrote: > On Thu, Apr 11, 2024 at 8:01 AM Krzysztof Kozlowski > <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > On 10/04/2024 23:26, Bjorn Helgaas wrote: > > > On Wed, Apr 10, 2024 at 08:15:19PM +0200, Krzysztof Kozlowski wrote: > > >> MT7621 PCI host bridge has children which apparently are also PCI host > > >> bridges, at least that's what the binding suggest. > > > > > > What does it even mean for a PCI host bridge to have a child that is > > > also a PCI host bridge? > > > > > > Does this mean a driver binds to the "parent" host bridge, enumerates > > > the PCI devices below it, and finds a "child" host bridge? > > Yes, that is exactly what you can see on enumeration. > > The following is a typical boot trace where all bridges has a device also below: > > mt7621-pci 1e140000.pcie: host bridge /pcie@1e140000 ranges: > mt7621-pci 1e140000.pcie: No bus range found for /pcie@1e140000, using [bus 00-ff] > mt7621-pci 1e140000.pcie: MEM 0x0060000000..0x006fffffff -> 0x0060000000 > mt7621-pci 1e140000.pcie: IO 0x001e160000..0x001e16ffff -> 0x0000000000 > mt7621-pci 1e140000.pcie: PCIE0 enabled > mt7621-pci 1e140000.pcie: PCIE1 enabled > mt7621-pci 1e140000.pcie: PCIE2 enabled > mt7621-pci 1e140000.pcie: PCI host bridge to bus 0000:00 1e140000.pcie is a host bridge. It has some CPU-specific bus on the upstream side, standard PCI (domain 0000, buses 00-ff) on the downstream side. > pci 0000:00:00.0: [0e8d:0801] type 01 class 0x060400 > pci 0000:00:01.0: [0e8d:0801] type 01 class 0x060400 > pci 0000:00:02.0: [0e8d:0801] type 01 class 0x060400 > pci 0000:01:00.0: [1b21:0611] type 00 class 0x010185 > pci 0000:00:00.0: PCI bridge to [bus 01-ff] > pci 0000:00:00.0: bridge window [io 0x0000-0x0fff] > pci 0000:00:00.0: bridge window [mem 0x00000000-0x000fffff] > pci 0000:00:00.0: bridge window [mem 0x00000000-0x000fffff pref] 00:00.0 looks like a PCIe Root Port to bus 01. This is not a host bridge; it's just a standard PCI-to-PCI bridge with PCI on both the upstream and downstream sides. > pci 0000:02:00.0: [1b21:0611] type 00 class 0x010185 > pci 0000:00:01.0: PCI bridge to [bus 02-ff] > pci 0000:00:01.0: bridge window [io 0x0000-0x0fff] > pci 0000:00:01.0: bridge window [mem 0x00000000-0x000fffff] > pci 0000:00:01.0: bridge window [mem 0x00000000-0x000fffff pref] 00:01.0 is another Root Port to bus 02. > pci 0000:03:00.0: [1b21:0611] type 00 class 0x010185 > pci 0000:00:02.0: PCI bridge to [bus 03-ff] > pci 0000:00:02.0: bridge window [io 0x0000-0x0fff] > pci 0000:00:02.0: bridge window [mem 0x00000000-0x000fffff] > pci 0000:00:02.0: bridge window [mem 0x00000000-0x000fffff pref] > pci_bus 0000:03: busn_res: [bus 03-ff] end is updated to 03 And 00:02.0 is a third Root Port to bus 03. > pci 0000:00:00.0: PCI bridge to [bus 01] > pci 0000:00:00.0: bridge window [io 0x0000-0x0fff] > pci 0000:00:00.0: bridge window [mem 0x60000000-0x600fffff] > pci 0000:00:00.0: bridge window [mem 0x60100000-0x601fffff pref] > pci 0000:00:01.0: PCI bridge to [bus 02] > pci 0000:00:01.0: bridge window [io 0x1000-0x1fff] > pci 0000:00:01.0: bridge window [mem 0x60200000-0x602fffff] > pci 0000:00:01.0: bridge window [mem 0x60300000-0x603fffff pref] > pci 0000:00:02.0: PCI bridge to [bus 03] > pci 0000:00:02.0: bridge window [io 0x2000-0x2fff] > pci 0000:00:02.0: bridge window [mem 0x60400000-0x604fffff] > > > I think the question should be towards Mediatek folks. I don't know what > > this hardware is exactly, just looks like pci-pci-bridge. The driver > > calls the children host bridges as "ports". > > You can see the topology here in my first driver submit cover letter > message [0]. > > [0]: https://lore.kernel.org/all/CAMhs-H-BA+KzEwuDPzcmrDPdgJBFA2XdYTBvT4R4MEOUB=WQ1g@xxxxxxxxxxxxxx/t/ Nothing unusual here, this looks like the standard PCIe topology. What *might* be unusual is describing the Root Ports in DT. Since they are standard PCI devices, they shouldn't need DT description unless there's some unusual power/clock/reset control or something that is not discoverable via PCI enumeration. Bjorn
