linux-kernel - Re: [PATCH v3 5/5] pci: Suspend iommu function prior to resetting a device

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Message-ID: <aLCvZOm11EAvrpx9@Asurada-Nvidia>
Date: Thu, 28 Aug 2025 12:35:00 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Ethan Zhao <etzhao1900@...il.com>, <robin.murphy@....com>,
	<joro@...tes.org>, <bhelgaas@...gle.com>, <will@...nel.org>,
	<robin.clark@....qualcomm.com>, <yong.wu@...iatek.com>,
	<matthias.bgg@...il.com>, <angelogioacchino.delregno@...labora.com>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<rafael@...nel.org>, <lenb@...nel.org>, <kevin.tian@...el.com>,
	<yi.l.liu@...el.com>, <baolu.lu@...ux.intel.com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
	<linux-mediatek@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<patches@...ts.linux.dev>, <pjaroszynski@...dia.com>, <vsethi@...dia.com>,
	<helgaas@...nel.org>
Subject: Re: [PATCH v3 5/5] pci: Suspend iommu function prior to resetting a
 device

On Thu, Aug 28, 2025 at 03:46:08PM -0300, Jason Gunthorpe wrote:
> On Thu, Aug 28, 2025 at 08:08:13AM -0700, Nicolin Chen wrote:
> > On Thu, Aug 28, 2025 at 09:51:49AM -0300, Jason Gunthorpe wrote:
> > > On Fri, Aug 22, 2025 at 11:50:58AM -0700, Nicolin Chen wrote:
> > > 
> > > > It feels like we need a no-fail re-attach operation, or at least an
> > > > unlikely-to-fail one. I recall years ago we tried a can_attach op
> > > > to test the compatibility but it didn't get merged. Maybe we'd need
> > > > it so that a concurrent attach can test compatibility, allowing the
> > > > re-attach in iommu_dev_reset_done() to more likely succeed.
> > > 
> > > This is probably the cleanest option to split these things
> > 
> > Yea, that could avoid failing a concurrent attach_dev during FLR
> > unless the dryrun fails, helping non-SRIOV cases too.
> > 
> > So, next version could have some new preparatory patches:
> >  - Pass in old domain to attach_dev
> >  - Add a can_attach_dev op
> 
> I wouldn't make this more complicated, just focus on the signal device
> case here then we move on from there
> 
> Just adding can_attach_dev is big series on its own

OK. I suppose a concurrent attach on a single device will be rare,
so failing it won't impact that much and thus can be a Part-1.

Then, for part-2, we will do can_attach_dev and support SRIOV.

Thanks
Nicolin