linux-kernel - Re: [PATCH 00/39] irqdomain: Simplify interrupt handling

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Message-ID: <87lf7t1ww5.wl-maz@kernel.org>
Date:   Tue, 01 Jun 2021 15:29:14 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Russell King <linux@...linux.org.uk>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH 00/39] irqdomain: Simplify interrupt handling

On Thu, 20 May 2021 17:37:12 +0100,
Marc Zyngier <maz@...nel.org> wrote:
> 
> Although most device drivers only deal with an interrupt number, the
> core IRQ code is mostly concerned with the irq_desc structure that
> describes the full interrupt context (hierarchy, handlers, state).
> 
> However, the low-level interrupt handling code that relies on the
> irqdomain abstraction has to perform an annoying dance to eventually
> get the core code to invoke interrupt handlers: the irqdomain code
> converts a low-level identifier to the unique Linux interrupt number,
> and the core code resolves this into an irq_desc pointer.
> 
> Each of these two lookups ends-up parsing a radix tree (although the
> irqdomain code can use a linear mapping for the smallest domains),
> which is obviously one too many. Wouldn't it be nice if the irqdomain
> would cache the irq_desc instead of forcing the core code to look it
> up on each and every interrupt? This is what this long series is all
> about.
> 
> There is roughly 3 parts here:
> 
> - a substantial amount of massaging for some architectures (nios, mips
>   and powerpc) to disentangle weird include constructs (asm/irq.h
>   including linux/irqdomain.h is pretty bad...) and simplify bits of
>   the irqdomain code
> 
> - some rework of the irqdomain code to allow the caching of a irq_data
>   pointer, unify the RCU behaviour and offer new APIs.
> 
> - Perform a bulk of conversions that turn constructs similar to
>   generic_handle_irq(irq_find_mapping(domain, hwirq)) into a simpler
>   call to generic_handle_domain_irq(domain, hwirq). Yes, this is a
>   mouthful.
> 
> I've kept most of the conversions per-subsystem/per-arch in order to
> keep the number of patches low (though it is debatable whether I have
> succeeded).
> 
> This ends up with a negative diffstat, so it can't be completely bad!
> Given the breadth of the changes, I do expect some breakage, although
> I've extensively compile-tested it and the kbuild robot has been
> invaluable in helping with the coverage.

Slight nudge in the direction of the cc'd arch maintainers. I'd like
to take the core of this series into -next (in practice, patches #1
through to #27). Any comment on the early, arch-specific patches would
be most welcome.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.