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

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Date:   Fri, 31 Dec 2021 18:13:51 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     Marc Zyngier <maz@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>, Leo Li <leoyang.li@....com>,
        Biwen Li <biwen.li@....com>, "Z.Q. Hou" <zhiqiang.hou@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2 devicetree] Revert "arm64: dts: freescale: Fix
 'interrupt-map' parent address cells"

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@kernel.org/
> 
> (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@kernel.org/
> 
> 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@....com>
> ---
> 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.