linux-kernel - Re: [PATCH 1/5] gpio: Don't fiddle with irqchips marked as immutable

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Date:   Thu, 24 Feb 2022 17:51:41 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Joey Gouly <joey.gouly@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/5] gpio: Don't fiddle with irqchips marked as immutable

On Wed, Feb 23, 2022 at 03:44:01PM +0000, Marc Zyngier wrote:
> In order to move away from gpiolib messing with the internals of
> unsuspecting irqchips, add a flag by which irqchips advertise
> that they are not to be messed with, and do solemnly swear that
> they correctly call into the gpiolib helpers wueh required.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  drivers/gpio/gpiolib.c | 7 ++++++-
>  include/linux/irq.h    | 2 ++
>  kernel/irq/debugfs.c   | 1 +
>  3 files changed, 9 insertions(+), 1 deletion(-)

I kind of like this. The bit where the const cast is essentially guarded
by an "immutable" flag is a bit funky, but it doesn't look like there is
a good way to do it by making all references const without doing a huge
all-at-once conversion.

I've always found it a bit irritating that irq_chip was somewhere
between a container for chip-specific data and an "ops" structure. I
think it'd be even nicer if this was split into an extra struct
irq_chip_ops, which could then always be const and a struct irq_chip
that contained primarily chip-specific data as well as a pointer to
struct irq_chip_ops.

But again, this seems fairly tricky to pull off given all the
interdependencies and we can iterate on this in the future, so this
seems like a good enough compromise:

Acked-by: Thierry Reding <treding@...dia.com>

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