Re: [PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[Thomas Gleixner]

On Tue, Mar 28 2023 at 07:48, Saurabh Singh Sengar wrote:
> On Tue, Mar 28, 2023 at 06:59:04AM -0700, H. Peter Anvin wrote:
>> 
>> Is there any reason why this variable can't be initialized to a fixed nonzero number, like 16?
>
> Yes, initializing gst_top to any non-zero value should fix this issue.
> At first I thought to intialize gst_top to 1.

That works only in your case. Some boot time registrations of IO_APICs
use gsi_top as the base. So initializing gsi_top to N would move IOAPIC[0]
interrupts out to irq N... and make the legacy interrupts fail.

That whole IOAPIC registration could do with some major cleanup, but
that's a different story.

Thanks,

        tglx