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

[Nicolin Chen]

On Tue, Nov 18, 2025 at 12:29:43AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc at nvidia.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 at nvidia.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 at nvidia.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".

Hmm, that's a fair point.

Having looked closely, I see only AMD and ARM call that to enable
ATs. How others (e.g. Intel) enable it?

And how do you think of the followings?

/*
 * Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software disables ATS before
 * initiating a reset. Though not all IOMMU drivers calls pci_enable_ats(), it
 * only gets invoked in IOMMU driver. And it is racy to check dev->ats_enabled
 * here, as a concurrent IOMMU attachment can enable ATS right after this line.
 *
 * Notify the IOMMU driver to stop IOMMU translations until the reset is done,
 * to ensure that the ATS function and its related invalidations are disabled.
 */

Thanks
Nicolin