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

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Message-ID: <4d3asssmv5xkttasl2xl2f6q3l5ki4jxmsrbyy6hvrd7djgsnj@y7drlazpwzi3>
Date: Tue, 9 Dec 2025 20:20:39 +0900
From: Manivannan Sadhasivam <mani@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
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 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.

- Mani

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