linux-kernel - Re: [PATCH] of: property: fw_devlink: Do not use interrupt-parent directly

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Message-ID: <CAL_JsqJ0K5z9rNHKNF1Xq8XnAkrxZaG-Th-e-G-zy5bo9_8=QA@mail.gmail.com>
Date: Tue, 19 Nov 2024 11:49:11 -0600
From: Rob Herring <robh@...nel.org>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: Saravana Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: property: fw_devlink: Do not use interrupt-parent directly

On Tue, Nov 19, 2024 at 10:47 AM Samuel Holland
<samuel.holland@...ive.com> wrote:
>
> Hi Rob,
>
> On 2024-11-19 9:41 AM, Rob Herring wrote:
> > On Thu, Nov 14, 2024 at 11:56:49AM -0800, Samuel Holland wrote:
> >> commit 7f00be96f125 ("of: property: Add device link support for
> >> interrupt-parent, dmas and -gpio(s)") started adding device links for
> >> the interrupt-parent property. Later, commit f265f06af194 ("of:
> >> property: Fix fw_devlink handling of interrupts/interrupts-extended")
> >> added full support for parsing the interrupts and interrupts-extended
> >> properties, which includes looking up the node of the parent domain.
> >> This made the handler for the interrupt-parent property redundant.
> >>
> >> In fact, creating device links based solely on interrupt-parent is
> >> problematic, because it can create spurious cycles. A node may have
> >> this property without itself being an interrupt controller or consumer.
> >> For example, this property is often present in the root node or a /soc
> >> bus node to set the default interrupt parent for child nodes. However,
> >> it is incorrect for the bus to depend on the interrupt controller, as
> >> some of the bus's childre may not be interrupt consumers at all or may
> >
> > typo
> >
> >> have a different interrupt parent.
> >>
> >> Resolving these spurious dependency cycles can cause an incorrect probe
> >> order for interrupt controller drivers. This was observed on a RISC-V
> >> system with both an APLIC and IMSIC under /soc, where interrupt-parent
> >> in /soc points to the APLIC, and the APLIC msi-parent points to the
> >> IMSIC. fw_devlink found three dependency cycles and attempted to probe
> >> the APLIC before the IMSIC. After applying this patch, there were no
> >> dependency cycles and the probe order was correct.
> >>
> >> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> >
> > I assume this should go to stable? It needs Fixes tags.
>
> What commit should I put in the Fixes tag? f265f06af194 ("of: property: Fix
> fw_devlink handling of interrupts/interrupts-extended"), because it finished
> making this code redundant? That commit didn't introduce any new bugs--this code
> was always wrong--but I would be hesitant to backport this change any further,
> because it might cause regressions without the "interrupts" property parsing in
> place.

I'd guess that f265f06af194 has been backported to everything with
7f00be96f125. I think we want either all 3 commits or none of them. If
something only works with a subset, then upstream is broken.

Rob