Re: [PATCH] PCI: Add quirk for ASPEED AST1150 bridge to prevent false RID aliasing

[Nirmoy Das]

On 17.12.25 14:48, Robin Murphy wrote:
> On 17/12/2025 1:32 pm, Nirmoy Das wrote:
> > ASPEED BMC controllers have VGA and USB functions behind a PCIe-to-PCI
> > bridge that causes them to share the same stream ID:
> >
> >    [e0]---00.0-[e1-e2]----00.0-[e2]--+-00.0  ASPEED Graphics Family
> >                                      \-02.0  ASPEED USB Controller
> >
> > Both devices get stream ID 0x5e200 due to bridge aliasing, causing the
> > USB controller to be rejected with 'Aliasing StreamID unsupported'.
> >
> > Per ASPEED, the AST1150 operates in PCI mode where downstream devices
> > generate their own distinct Requester IDs. Set
> > PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT to stop false alias detection.
>
> I don't think that's really the right quirk - that one effectively 
> means "RID aliasing upstream of this bridge is irrelevant", whereas 
> what you want here is "RID aliasing *at* this bridge doesn't happen 
> even though it looks like it could". With BRIDGE_XLATE_ROOT, I think 
> if you then put this behind a contrived upstream chain of additional 
> PCIe->PCI->PCIE bridges that *could* legitimately introduce further 
> aliasing, it would give the wrong result.

Thanks Robin. You're right - I'll send a v2 using the a new 
PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES quirk Jason suggested, which 
correctly handles only aliasing at this bridge.


> Thanks,
> Robin.
>
> > Signed-off-by: Nirmoy Das <nirmoyd@xxxxxxxxxx>
> > ---
> >   drivers/pci/quirks.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index b9c252aa6fe0..a7a1bf4c4354 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4453,6 +4453,20 @@ 
> > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9000,
> >   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9084,
> >                   quirk_bridge_cavm_thrx2_pcie_root);
> >   +/*
> > + * ASPEED AST1150 is a PCIe-to-PCI bridge that operates in PCI mode 
> > (not PCI-X).
> > + * Although it reports as a PCIe-to-PCI bridge, the downstream PCI 
> > bus does not
> > + * perform conventional Requester ID aliasing - each device behind 
> > the bridge
> > + * generates its own distinct Requester ID. This quirk stops false 
> > alias
> > + * detection at the bridge, fixing IOMMU StreamID conflicts that 
> > break DMA for
> > + * devices like the USB controller behind this bridge.
> > + */
> > +static void quirk_aspeed_ast1150_bridge(struct pci_dev *pdev)
> > +{
> > +    pdev->dev_flags |= PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT;
> > +}
> > +DECLARE_PCI_FIXUP_HEADER(0x1a03, 0x1150, quirk_aspeed_ast1150_bridge);
> > +
> >   /*
> >    * Intersil/Techwell TW686[4589]-based video capture cards have an 
> > empty (zero)
> >    * class code.  Fix it.