linux-kernel - Re: [PATCH v2 3/4] PCI: Disable ACS SV capability for the broken IDT switches

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Message-ID: <20251217151952.GG31492@ziepe.ca>
Date: Wed, 17 Dec 2025 11:19:52 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
	Xingang Wang <wangxingang5@...wei.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2 3/4] PCI: Disable ACS SV capability for the broken IDT
 switches

On Tue, Dec 09, 2025 at 08:20:39PM +0900, Manivannan Sadhasivam wrote:
> On Tue, Dec 02, 2025 at 03:15:33PM -0400, Jason Gunthorpe wrote:
> > On Tue, Dec 02, 2025 at 07:52:50PM +0530, Manivannan Sadhasivam wrote:
> > > @@ -544,6 +544,7 @@ struct pci_dev {
> > >  #endif
> > >  	u16		acs_cap;	/* ACS Capability offset */
> > >  	u16		acs_capabilities; /* ACS Capabilities */
> > > +	u16		acs_broken_cap; /* Broken ACS Capabilities */
> > 
> > Why do we need this? Have the quirk function accep tthe
> > acs_capabilities from the register and return the value to program
> > into struct pci_dev ?
> > 
> 
> We dont have any quirk levels between pci_acs_init() and pci_acs_enable() that
> will allow us to modify pci_dev::acs_capabilities in the quirk function. Hence,
> I came up with one more member to pass the broken caps.

Call the quirk function directly from the ACS path? We have things
like that already for ACS?

Jason