Re: [RFC PATCH kernel] powerpc/xive: Drop deregistered irqs

On 14/07/2019 03:31, Benjamin Herrenschmidt wrote:

On Sat, 2019-07-13 at 18:53 +1000, Alexey Kardashevskiy wrote:

quoted

On 13/07/2019 09:47, Benjamin Herrenschmidt wrote:

quoted

On Fri, 2019-07-12 at 19:37 +1000, Alexey Kardashevskiy wrote:

quoted

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/irq.c#n614

quoted

quoted

quoted

If so, then in order to do EOI, I'll need the desc which is gone,
or
I am missing the point?

All you need is drop the local CPU priority.

I know that, the question was how. I cannot use irq_chip in
arch/powerpc/kernel/irq.c and I do not want to add
ppc_md.enable_irqs().

Well, best is probably to do just that though, but call it something
like ppc_md.orphan_irq() or something like that instead. Another option
as you mention is to try to scrub queues, but that's trickier to do due
to the lockless nature of the queue handling.

When the IRQ is shutdown, couldn't we cleanup the CPU EQ by filtering 
all the dangling entries, and replacing them with zeroes ? That would
be alternative 1, but I don't think we need to scan all cpus. The last
target should be enough.

C.