linux-kernel - Re: [PATCH v2 2/2] PCI: Add PCI_BRIDGE_NO

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Message-ID: <20251217160133.GQ6079@nvidia.com>
Date: Wed, 17 Dec 2025 12:01:33 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nirmoy Das <nirmoyd@...dia.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
	Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
	iommu@...ts.linux.dev, jammy_huang@...eedtech.com, mochs@...dia.com
Subject: Re: [PATCH v2 2/2] PCI: Add PCI_BRIDGE_NO_ALIASES quirk for ASPEED
 AST1150

On Wed, Dec 17, 2025 at 07:45:29AM -0800, 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.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nirmoy Das <nirmoyd@...dia.com>
> ---
> 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(+)

I bet there will be more aspeed devices to come, but this is a
reasonable start

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Thanks,
Jason