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

On Thu, Dec 9, 2021 at 7:16 PM Lad, Prabhakar
[off-list ref] wrote:

On Thu, Dec 9, 2021 at 8:34 PM Rob Herring [off-list ref] wrote:

quoted

On Thu, Dec 9, 2021 at 5:35 AM Lad, Prabhakar
[off-list ref] wrote:

quoted

Hi Rob and Marc,

On Thu, Dec 9, 2021 at 10:33 AM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 09 Dec 2021 10:00:44 +0000,
"Lad, Prabhakar" [off-list ref] wrote:

quoted

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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.

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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