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

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Message-ID: <aRt2/0rcdjcGk1Z1@Asurada-Nvidia>
Date: Mon, 17 Nov 2025 11:26:55 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
CC: "joro@...tes.org" <joro@...tes.org>, "afael@...nel.org"
	<afael@...nel.org>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"alex@...zbot.org" <alex@...zbot.org>, "jgg@...dia.com" <jgg@...dia.com>,
	"will@...nel.org" <will@...nel.org>, "robin.murphy@....com"
	<robin.murphy@....com>, "lenb@...nel.org" <lenb@...nel.org>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-acpi@...r.kernel.org"
	<linux-acpi@...r.kernel.org>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>, "Jaroszynski, Piotr"
	<pjaroszynski@...dia.com>, "Sethi, Vikram" <vsethi@...dia.com>,
	"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

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.

> > > > +	/* Have to call it after waiting for pending DMA transaction */
> > > > +	ret = pci_reset_iommu_prepare(dev);
> > > > +	if (ret) {
> > > > +		pci_err(dev, "failed to stop IOMMU\n");
> > >
> > > the error message could be more informative.
> > 
> > OK. Perhaps print the ret value.
> > 
> 
> and mention that it's for PCI reset.

OK.

Thanks
Nicolin