Re: [BUG] rockpro64: PCI BAR reassignment broken by commit 9d57e61bf723 ("of/pci: Add IORESOURCE_MEM_64 to resource flags for 64-bit memory addresses")

[Ard Biesheuvel]

On Tue, 25 May 2021 at 15:42, Punit Agrawal <punitagrawal@xxxxxxxxx> wrote:
>
> Hi Ard,
>
> Ard Biesheuvel <ardb@xxxxxxxxxx> writes:
>
> > On Sun, 23 May 2021 at 13:06, Punit Agrawal <punitagrawal@xxxxxxxxx> wrote:
> >>
> >> Robin Murphy <robin.murphy@xxxxxxx> writes:
> >>
> >> > [ +linux-pci for visibility ]
> >> >
> >> > On 2021-05-18 10:09, Alexandru Elisei wrote:
> >> >> After doing a git bisect I was able to trace the following error when booting my
> >> >> rockpro64 v2 (rk3399 SoC) with a PCIE NVME expansion card:
> >> >> [..]
> >> >> [    0.305183] rockchip-pcie f8000000.pcie: host bridge /pcie@f8000000 ranges:
> >> >> [    0.305248] rockchip-pcie f8000000.pcie:      MEM 0x00fa000000..0x00fbdfffff ->
> >> >> 0x00fa000000
> >> >> [    0.305285] rockchip-pcie f8000000.pcie:       IO 0x00fbe00000..0x00fbefffff ->
> >> >> 0x00fbe00000
> >> >> [    0.306201] rockchip-pcie f8000000.pcie: supply vpcie1v8 not found, using dummy
> >> >> regulator
> >> >> [    0.306334] rockchip-pcie f8000000.pcie: supply vpcie0v9 not found, using dummy
> >> >> regulator
> >> >> [    0.373705] rockchip-pcie f8000000.pcie: PCI host bridge to bus 0000:00
> >> >> [    0.373730] pci_bus 0000:00: root bus resource [bus 00-1f]
> >> >> [    0.373751] pci_bus 0000:00: root bus resource [mem 0xfa000000-0xfbdfffff 64bit]
> >> >> [    0.373777] pci_bus 0000:00: root bus resource [io  0x0000-0xfffff] (bus
> >> >> address [0xfbe00000-0xfbefffff])
> >> >> [    0.373839] pci 0000:00:00.0: [1d87:0100] type 01 class 0x060400
> >> >> [    0.373973] pci 0000:00:00.0: supports D1
> >> >> [    0.373992] pci 0000:00:00.0: PME# supported from D0 D1 D3hot
> >> >> [    0.378518] pci 0000:00:00.0: bridge configuration invalid ([bus 00-00]),
> >> >> reconfiguring
> >> >> [    0.378765] pci 0000:01:00.0: [144d:a808] type 00 class 0x010802
> >> >> [    0.378869] pci 0000:01:00.0: reg 0x10: [mem 0x00000000-0x00003fff 64bit]
> >> >> [    0.379051] pci 0000:01:00.0: Max Payload Size set to 256 (was 128, max 256)
> >> >> [    0.379661] pci 0000:01:00.0: 8.000 Gb/s available PCIe bandwidth, limited by
> >> >> 2.5 GT/s PCIe x4 link at 0000:00:00.0 (capable of 31.504 Gb/s with 8.0 GT/s PCIe
> >> >> x4 link)
> >> >> [    0.393269] pci_bus 0000:01: busn_res: [bus 01-1f] end is updated to 01
> >> >> [    0.393311] pci 0000:00:00.0: BAR 14: no space for [mem size 0x00100000]
> >> >> [    0.393333] pci 0000:00:00.0: BAR 14: failed to assign [mem size 0x00100000]
> >> >> [    0.393356] pci 0000:01:00.0: BAR 0: no space for [mem size 0x00004000 64bit]
> >> >> [    0.393375] pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x00004000 64bit]
> >> >> [    0.393397] pci 0000:00:00.0: PCI bridge to [bus 01]
> >> >> [    0.393839] pcieport 0000:00:00.0: PME: Signaling with IRQ 78
> >> >> [    0.394165] pcieport 0000:00:00.0: AER: enabled with IRQ 78
> >> >> [..]
> >> >> to the commit 9d57e61bf723 ("of/pci: Add IORESOURCE_MEM_64 to
> >> >> resource flags for
> >> >> 64-bit memory addresses").
> >> >
> >> > FWFW, my hunch is that the host bridge advertising no 32-bit memory
> >> > resource, only only a single 64-bit non-prefetchable one (even though
> >> > it's entirely below 4GB) might be a bit weird and tripping something
> >> > up in the resource assignment code. It certainly seems like the thing
> >> > most directly related to the offending commit.
> >> >
> >> > I'd be tempted to try fiddling with that in the DT (i.e. changing
> >> > 0x83000000 to 0x82000000 in the PCIe node's "ranges" property) to see
> >> > if it makes any difference. Note that even if it helps, though, I
> >> > don't know whether that's the correct fix or just a bodge around a
> >> > corner-case bug somewhere in the resource code.
> >>
> >> From digging into this further the failure seems to be due to a mismatch
> >> of flags when allocating resources in pci_bus_alloc_from_region() -
> >>
> >>     if ((res->flags ^ r->flags) & type_mask)
> >>             continue;
> >>
> >> Though I am also not sure why the failure is only being reported on
> >> RK3399 - does a single 64-bit window have anything to do with it?
> >>
> >
> > The NVMe in the example exposes a single 64-bit non-prefetchable BAR.
> > Such BARs can not be allocated in a prefetchable host bridge window
> > (unlike the converse, i.e., allocating a prefetchable BAR in a
> > non-prefetchable host bridge window is fine)
> >
> > 64-bit non-prefetchable host bridge windows cannot be forwarded by PCI
> > to PCI bridges, they simply lack the BAR registers to describe them.
> > Therefore, non-prefetchable endpoint BARs (even 64-bit ones) need to
> > be carved out of a host bridge's non-prefetchable 32-bit window if
> > they need to pass through a bridge.
>
> Thank you for the explanation. I also looked at the PCI-to-PCI Bridge
> spec to understand where some of the limitations are coming from.
>
> > So the error seems to be here that the host bridge's 32-bit
> > non-prefetchable window has the 64-bit attribute set, even though it
> > resides below 4 GB entirely. I suppose that the resource allocation
> > could be made more forgiving (and it was in the past, before commit
> > 9d57e61bf723 was applied). However, I would strongly recommend not
> > deviating from common practice, and just describe the 32-bit
> > addressable non-prefetchable resource window as such.
>
> IIUC, the host bridge's configuration (64-bit on non-prefetchable
> window) is based on what the hardware advertises.
>

What do you mean by 'what the hardware advertises'? The host bridge is
apparently configured to decode a 32-bit addressable window as MMIO,
and the question is why this window has the 64-bit attribute set in
the DT description.

> Can you elaborate on what you have in mind to correct the
> non-prefetchable resource window? Are you thinking of adding a quirk
> somewhere to address this?
>

No. Just fix the DT.

> I am happy to put something together once I understand the preferred way
> to go about it.
>
> Thanks,
> Punit
>
> [...]
>