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

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Sat, Apr 23, 2022 at 12:30 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Fri, 22 Apr 2022 22:24:22 +0100,
> Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> >
> > On Tue, Apr 19, 2022 at 4:19 PM Marc Zyngier <maz@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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.

I would prefer it if it goes as is now and every stakeholder can just
pull it. As far as my drivers are concerned I also want to convert
them sooner than later, meaning I want to pull this into my little
tree as well. Bart, Linus, would it be also preferable for you?


-- 
With Best Regards,
Andy Shevchenko