linux-kernel - RE: [PATCH v5 5/5] pci: Suspend iommu function prior to resetting a device

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Message-ID: <BN9PR11MB527649AD7D251EAAFDFB753A8CD6A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 18 Nov 2025 00:29:43 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>
CC: "joro@...tes.org" <joro@...tes.org>, "afael@...nel.org"
	<afael@...nel.org>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
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	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
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	<linux-acpi@...r.kernel.org>, "linux-pci@...r.kernel.org"
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	"patches@...ts.linux.dev" <patches@...ts.linux.dev>, "Jaroszynski, Piotr"
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	"helgaas@...nel.org" <helgaas@...nel.org>, "etzhao1900@...il.com"
	<etzhao1900@...il.com>
Subject: RE: [PATCH v5 5/5] pci: Suspend iommu function prior to resetting a
 device

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Tuesday, November 18, 2025 3:27 AM
> 
> On Mon, Nov 17, 2025 at 04:52:05AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Saturday, November 15, 2025 2:01 AM
> > >
> > > On Fri, Nov 14, 2025 at 09:45:31AM +0000, Tian, Kevin wrote:
> > > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > > Sent: Tuesday, November 11, 2025 1:13 PM
> > > > >
> > > > > +/*
> > > > > + * Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software
> disables
> > > ATS
> > > > > before
> > > > > + * initiating a reset. Notify the iommu driver that enabled ATS.
> > > > > + */
> > > > > +int pci_reset_iommu_prepare(struct pci_dev *dev)
> > > > > +{
> > > > > +	if (pci_ats_supported(dev))
> > > > > +		return iommu_dev_reset_prepare(&dev->dev);
> > > > > +	return 0;
> > > > > +}
> > > >
> > > > the comment says "driver that enabled ATS", but the code checks
> > > > whether ATS is supported.
> > > >
> > > > which one is desired?
> > >
> > > The comments says "the iommu driver that enabled ATS". It doesn't
> > > conflict with what the PCI core checks here?
> >
> > actually this is sent to all IOMMU drivers. there is no check on whether
> > a specific driver has enabled ATS in this path.
> 
> But the comment doesn't say "check"..
> 
> How about "Notify the iommu driver that enables/disables ATS"?
> 
> The point is that pci_enable_ats() is called in iommu drivers.
> 

but in current way even an iommu driver which doesn't call
pci_enable_ats() will also be notified then I didn't see the
point of adding an attribute to "the iommu driver".