Re: [PATCH v2 2/2] PCI: Add PCI_BRIDGE_NO_ALIASES quirk for ASPEED AST1150

[Nirmoy Das]

On 17.12.25 19:07, Robin Murphy wrote:
> On 17/12/2025 3:45 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 doesn't use a real PCI bus and always forwards
> > the original requester ID from downstream devices rather than replacing
> > it with any alias.
> >
> > Add a new PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES flag and apply it to the
> > AST1150.
>
> Looks reasonable to me;
>
> Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
>
> (Super-nit: perhaps s/ALIASES/ALIAS/ to neatly mirror 
> PCI_DEV_FLAG_PCIE_BRIDGE_ALIAS, which amusingly it's pretty much the 
> exact opposite of, but I'll leave that to Bjorn's discretion)


Thanks Robin! Happy to resend with s/ALIASES/ALIAS/ if Bjorn prefers.

> > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Signed-off-by: Nirmoy Das <nirmoyd@xxxxxxxxxx>
> > ---
> > v2:
> >    - Use new PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES flag instead of
> >      PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT to only skip aliasing at this
> >      bridge, not stop the entire upstream alias walk (Jason Gunthorpe)
> >
> >   drivers/pci/quirks.c | 10 ++++++++++
> >   drivers/pci/search.c |  2 ++
> >   include/linux/pci.h  |  5 +++++
> >   3 files changed, 17 insertions(+)
> >
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index b9c252aa6fe0..a37b7305ae5f 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4453,6 +4453,16 @@ 
> > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9000,
> >   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9084,
> >                   quirk_bridge_cavm_thrx2_pcie_root);
> >   +/*
> > + * AST1150 doesn't use a real PCI bus and always forwards the 
> > requester ID
> > + * from downstream devices.
> > + */
> > +static void quirk_aspeed_pci_bridge_no_aliases(struct pci_dev *pdev)
> > +{
> > +    pdev->dev_flags |= PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES;
> > +}
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ASPEED, 0x1150, 
> > quirk_aspeed_pci_bridge_no_aliases);
> > +
> >   /*
> >    * Intersil/Techwell TW686[4589]-based video capture cards have an 
> > empty (zero)
> >    * class code.  Fix it.
> > diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> > index 53840634fbfc..2f44444ae22f 100644
> > --- a/drivers/pci/search.c
> > +++ b/drivers/pci/search.c
> > @@ -86,6 +86,8 @@ int pci_for_each_dma_alias(struct pci_dev *pdev,
> >               case PCI_EXP_TYPE_DOWNSTREAM:
> >                   continue;
> >               case PCI_EXP_TYPE_PCI_BRIDGE:
> > +                if (tmp->dev_flags & 
> > PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES)
> > +                    continue;
> >                   ret = fn(tmp,
> >                        PCI_DEVID(tmp->subordinate->number,
> >                              PCI_DEVFN(0, 0)), data);
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index b16127c6a7b4..963da06ef193 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -248,6 +248,11 @@ enum pci_dev_flags {
> >       PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 
> > 12),
> >       /* Device requires write to PCI_MSIX_ENTRY_DATA before any MSIX 
> > reads */
> >       PCI_DEV_FLAGS_MSIX_TOUCH_ENTRY_DATA_FIRST = (__force 
> > pci_dev_flags_t) (1 << 13),
> > +    /*
> > +     * PCIe to PCI bridge does not create RID aliases because the 
> > bridge is
> > +     * integrated with the downstream devices and doesn't use real PCI.
> > +     */
> > +    PCI_DEV_FLAGS_PCI_BRIDGE_NO_ALIASES = (__force pci_dev_flags_t) 
> > (1 << 14),
> >   };
> >     enum pci_irq_reroute_variant {