linux-kernel - Re: [tip: irq/msi] PCI: dwc: Enable MSI affinity support

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Message-ID: <9ec6928cd4e7a599d4bbb6ac0258da8997518d3a.camel@redhat.com>
Date: Tue, 06 Jan 2026 10:07:12 -0500
From: Radu Rendec <rrendec@...hat.com>
To: Jon Hunter <jonathanh@...dia.com>, linux-kernel@...r.kernel.org, 
	linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org, 
 "linux-tegra@...r.kernel.org"
	 <linux-tegra@...r.kernel.org>
Subject: Re: [tip: irq/msi] PCI: dwc: Enable MSI affinity support

Hi Jon,

On Tue, 2026-01-06 at 09:53 +0000, Jon Hunter wrote:
> On 15/12/2025 21:34, tip-bot2 for Radu Rendec wrote:
> > The following commit has been merged into the irq/msi branch of tip:
> > 
> > Commit-ID:     eaf290c404f7c39f23292e9ce83b8b5b51ab598a
> > Gitweb:        https://git.kernel.org/tip/eaf290c404f7c39f23292e9ce83b8b5b51ab598a
> > Author:        Radu Rendec <rrendec@...hat.com>
> > AuthorDate:    Fri, 28 Nov 2025 16:20:55 -05:00
> > Committer:     Thomas Gleixner <tglx@...utronix.de>
> > CommitterDate: Mon, 15 Dec 2025 22:30:48 +01:00
> > 
> > PCI: dwc: Enable MSI affinity support
> > 
> > Leverage the interrupt redirection infrastructure to enable CPU affinity
> > support for MSI interrupts. Since the parent interrupt affinity cannot
> > be changed, affinity control for the child interrupt (MSI) is achieved
> > by redirecting the handler to run in IRQ work context on the target CPU.
> > 
> > This patch was originally prepared by Thomas Gleixner (see Link tag below)
> > in a patch series that was never submitted as is, and only parts of that
> > series have made it upstream so far.
> > 
> > Originally-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Radu Rendec <rrendec@...hat.com>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Link: https://lore.kernel.org/linux-pci/878qpg4o4t.ffs@tglx/
> > Link: https://patch.msgid.link/20251128212055.1409093-4-rrendec@redhat.com
> 
> 
> With next-20260105 I am observing the following warning on the Tegra194 
> Jetson AGX platform ...
> 
>   WARNING KERN genirq: irq_chip DW-PCI-MSI-0001:01:00.0 did not update
>    eff. affinity mask of irq 171
> 
> Bisect is point to this commit. This platform is using the driver 
> drivers/pci/controller/dwc/pcie-tegra194.c. Is there some default 
> affinity that we should be setting to avoid this warning?

Before that patch, affinity control wasn't even possible for PCI MSIs
exposed by the dw_pci drivers. Without having looked at the code yet,
I suspect it's just because now that affinity control is enabled,
something tries to use it.

I don't think you should set some default affinity. By default, the PCI
MSIs should be affine to all available CPUs, and that warning shouldn't
happen in the first place. Let me test on Jetson AGX and see what's
going on. I'll update the thread with my findings, hopefully later
today.

-- 
Thanks,
Radu