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

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Message-ID: <15a6ecb8-ca6b-46bd-a065-0f35c488628e@sifive.com>
Date: Wed, 20 Nov 2024 16:58:25 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Rob Herring <robh@...nel.org>
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 2024-11-19 11:49 AM, Rob Herring wrote:
> 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.

Of the current LTS branches, v5.10 has only 7f00be96f125. f265f06af194 was only
backported as far as v5.15, since it Fixes: 4104ca776ba3 ("of: property: Add
fw_devlink support for interrupts"), which was merged for v5.12. I will add this
same Fixes: tag for v2.

Regards,
Samuel