Re: Affinity for GIC irq line

From: valmiki
Date: Wed Apr 25 2018 - 23:49:54 EST

On 25/04/18 04:23, valmiki wrote:
Hi all,

When an IRQ line is set affinity using irq_set_affinity, which calls
irq_do_set_affinity, this API copies affinity mask to affinity variable
in irq_common_data of this irq descriptor.

It does a wee bit more. Crucially, it contains the line:

ret = chip->irq_set_affinity(data, mask, force);
Yes, i overlooked this part.

But as per ARM GICv2 document in order to drive a interrupt to a
specific CPU we need to program GICD_ITARGETSRn register.

But irq_set_affinity isn't writing to this register.Please correct me if
I'm wrong i did not find code for this register being updated in
irq_set_affinity flow.
So how affinity is being set for an IRQ line ?

I would have though that a function name such as "gic_set_affinity" was
clear enough?

If affinity was set successfully on what CPU does asm_do_IRQ run ?

It runs on the CPU that the interrupt targets, I'd say.
Thanks Marc.
How does affinity for virtual irq work ?
For example pci-xgene-msi.c has xgene_msi_set_affinity function which sets affinity for each virq.
As per arm64/boot/dts/apm/apm-storm.dtsi they use GICv2.
They are trying to map each virq to specific cpu but already GIC lines affinity is set, when this affinity would be used ?

What does
/* Update MSI number to target the new CPU */
irqdata->hwirq = hwirq_to_canonical_hwirq(irqdata->hwirq) + target_cpu;

the above code do ?
Already mapping for hwirq to virq is done by this time for this domain.
Now if hwirq is updated its mapping doesn't it lead to wrong virq ?


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