Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures

Marc Zyngier
2022-04-23T10:30:34Z

On Fri, 22 Apr 2022 22:24:22 +0100,
Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Tue, Apr 19, 2022 at 4:19 PM Marc Zyngier <maz@kernel.org> wrote:
>
> > This is a followup from [2].
> >
> > I recently realised that the gpiolib play ugly tricks on the
> > unsuspecting irq_chip structures by patching the callbacks.
> >
> > Not only this breaks when an irq_chip structure is made const (which
> > really should be the default case), but it also forces this structure
> > to be copied at nauseam for each instance of the GPIO block, which is
> > a waste of memory.
> >
> > My current approach is to add a new irq_chip flag (IRQCHIP_IMMUTABLE)
> > which does what it says on the tin: don't you dare writing to them.
> > Gpiolib is further updated not to install its own callbacks, and it
> > becomes the responsibility of the driver to call into the gpiolib when
> > required. This is similar to what we do for other subsystems such as
> > PCI-MSI.
> >
> > 5 drivers are updated to this new model: M1, QC, Tegra, pl061 and AMD
> > (as I actively use them) keeping a single irq_chip structure, marking
> > it const, and exposing the new flag.
> >
> > Nothing breaks, the volume of change is small, the memory usage goes
> > down and we have fewer callbacks that can be used as attack vectors.
> > What's not to love?
> >
> > Since there wasn't any objection in the previous round of review, I'm
> > going to take this series into -next to see if anything breaks at
> > scale.
>
> The series:
> Acked-by: Linus Walleij <linus.walleij@linaro.org>
>
> Bartosz: if you're happy with this can you apply it to an immutable branch
> from v5.18-rc1 and merge that into the GPIO for-next and then I can also
> pull that into pinctrl?

For what it is worth, I've pushed this branch into irqchip-next.

You can pick it up from:

https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/gpio-immutable

but I can also drop it from the irqchip tree.

Just let me know.

M.

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