Re: [PATCH v2 devicetree] Revert "arm64: dts: freescale: Fix 'interrupt-map' parent address cells"

[Marc Zyngier]

On 2021-12-31 18:13, Vladimir Oltean wrote:
> Hello,
>
> On Tue, Dec 14, 2021 at 03:58:52PM +0200, Vladimir Oltean wrote:
> > This reverts commit 869f0ec048dc8fd88c0b2003373bd985795179fb. That
> > updated the expected device tree binding format for the ls-extirq
> > driver, without also updating the parsing code (ls_extirq_parse_map)
> > to the new format.
> >
> > The context is that the ls-extirq driver uses the standard
> > "interrupt-map" OF property in a non-standard way, as suggested by
> > Rob Herring during review:
> > https://lore.kernel.org/lkml/20190927161118.GA19333@bogus/
> >
> > This has turned out to be problematic, as Marc Zyngier discovered
> > through commit 041284181226 ("of/irq: Allow matching of an 
> > interrupt-map
> > local to an interrupt controller"), later fixed through commit
> > de4adddcbcc2 ("of/irq: Add a quirk for controllers with their own
> > definition of interrupt-map"). Marc's position, expressed on multiple
> > opportunities, is that:
> >
> > (a) [ making private use of the reserved "interrupt-map" name in a
> >     driver ] "is wrong, by the very letter of what an interrupt-map
> >     means. If the interrupt map points to an interrupt controller,
> >     that's the target for the interrupt."
> > https://lore.kernel.org/lkml/87k0g8jlmg.wl-maz@xxxxxxxxxx/
> >
> > (b) [ updating the driver's bindings to accept a non-reserved name for
> >     this property, as an alternative, is ] "is totally pointless. 
> > These
> >     machines have been in the wild for years, and existing DTs will be
> >     there *forever*."
> > https://lore.kernel.org/lkml/87ilvrk1r0.wl-maz@xxxxxxxxxx/
> >
> > Considering the above, the Linux kernel has quirks in place to deal 
> > with
> > the ls-extirq's non-standard use of the "interrupt-map". These quirks
> > may be needed in other operating systems that consume this device 
> > tree,
> > yet this is seen as the only viable solution.
> >
> > Therefore, the premise of the patch being reverted here is invalid.
> > It doesn't matter whether the driver, in its non-standard use of the
> > property, complies to the standard format or not, since this property
> > isn't expected to be used for interrupt translation by the core.
> >
> > This change restores LS1088A, LS2088A/LS2085A and LX2160A to their
> > previous bindings, which allows these systems to continue to use
> > external interrupt lines with the correct polarity.
> >
> > Fixes: 869f0ec048dc ("arm64: dts: freescale: Fix 'interrupt-map' 
> > parent address cells")
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> > ---
> > v1->v2: remove the other 9 patches that rename "interrupt-map" to
> >         "fsl,extirq-map", at Marc's suggestion.
>
> Could this patch be considered for merging in v5.16? The problem is
> going to be quite a bit more severe and tricky to fix otherwise. 
> Thanks.

FWIW:

Acked-by: Marc Zyngier <maz@xxxxxxxxxx>

Rob, Shawn, can you please queue this as an urgent fix for 5.16?

Thanks,

        M.
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