Re: [RFC PATCH] of: platform: Skip mapping of interrupts in of_device_alloc()

[Rob Herring <robh+dt@kernel.org>]

On Thu, Dec 9, 2021 at 7:16 PM Lad, Prabhakar
<prabhakar.csengg@gmail.com> wrote:
>
> On Thu, Dec 9, 2021 at 8:34 PM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > On Thu, Dec 9, 2021 at 5:35 AM Lad, Prabhakar
> > <prabhakar.csengg@gmail.com> wrote:
> > >
> > > Hi Rob and Marc,
> > >
> > > On Thu, Dec 9, 2021 at 10:33 AM Marc Zyngier <maz@kernel.org> wrote:
> > > >
> > > > On Thu, 09 Dec 2021 10:00:44 +0000,
> > > > "Lad, Prabhakar" <prabhakar.csengg@gmail.com> wrote:
> > > > >
> > > > > > The root of the issue is that all the resource allocation is done
> > > > > > upfront, way before we even have a driver that could potentially
> > > > > > deal with this device. This is a potential waste of resource, and
> > > > > > it triggers the issue you noticed.
> > > > > >
> > > > > > If you delay the resource allocation until there is an actual
> > > > > > match with a driver, you could have a per-driver flag telling you
> > > > > > whether the IRQ allocation should be performed before the probe()
> > > > > > function is called.
> > > > > >
> > > > > As suggested by Rob, if we switch the drivers to use
> > > > > platform_get_resource(pdev, IORESOURCE_IRQ, n) call with
> > > > > platform_get_irq() this code should go away and with this switch the
> > > > > resource allocation will happen demand. Is this approach OK?
> > > >
> > > > If you get rid of of_irq_to_resource_table() altogether, then yes,
> > > > this has a fighting chance to work.
> > > >
> > > Yes, switching to platform_get_irq() will eventually cause
> > > of_irq_to_resource_table() to go away.
> > >
> > > On second thought, instead of touching all the drivers, if we update
> > > platform_get_resource/platform_get_resource_byname to internally call
> > > platform_get_irq() internally if it's a IORESOURCE_IRQ resource. Does
> > > that sound good or should I just get on changing all the drivers to
> > > use platform_get_irq() instead?
> >
> > Except that platform_get_irq() already internally calls
> > platform_get_resource()... I think changing the drivers is the right
> > way. Happy to do some if you want to divide it up.
> >
> Thank you, I think I'll manage.
>
> > Using coccigrep, I think I've found all the places using
> > platform_device.resource directly. A large swath are Sparc drivers
> > which don't matter. The few that do matter I've prepared patches for
> > here[1]. Most of what I found were DT based drivers that copy
> > resources to a child platform device. That case will not work with
> > platform_get_irq() callers either unless the child device has it's DT
> > node set to the parent node which is the change I made.
> >
> Thank you for getting this done. Do you want me to include those along
> with my conversion patches?

No, I'll send them out.

> Any reason why we dont care for Sparc drivers?

Sparc does its own thing and doesn't use drivers/of/platform.c to
create devices. I'm sure we could modernize a bunch of them, but
that's not a blocker.

Rob