Re: Interrupts in pci-aardvark

[Marc Zyngier <maz@kernel.org>]

On Sun, 28 Mar 2021 15:09:12 +0100,
Pali Rohár <pali@kernel.org> wrote:

[...]

> Aardvark HW allows to mask summary TOP, summary CORE, individual CORE
> (PME, ERR, INTA, INTB, ...), summary MSI and individual MSI bits
> interrupts, but not final 16 bit MSI interrupt number. MSI bits are low
> 5 bits of 16 bit interrupt number. So it is not possible to mask or
> unmask MSI interrupt number X. It is possible to only mask/unmask all
> MSI interrupts which low 5 bits is specific value.

If you cannot mask individual MSIs, you have two choices:

- you only support MSI-X *or* MSI (not multi-MSI) and mask interrupts
  at the device level

- you restrict the number of MSIs to those you can actually control,
  and that's 2^5 = 32 (which is what the driver currently supports, I
  believe).

> 
> Also aardvark HW allows to globally enable / disable processing of MSI
> interrupts. Masking summary MSI interrupt just cause that GIC does not
> trigger it but from registers I can read it (e.g. when GIC calls
> aardvark interrupt handler for other non-MSI interrupt).
> 
> And I would like to ask, what is in this hierarchy from kernel point of
> view "bottom part of MSI" and what is the "upper part of MSI"? As in
> above diagram there are 3 MSI layers.

The upper part is the bus-specific part, PCI in your case. You don't
need to implement it.

The bottom part controls the HW, and deals with all the masking,
acknoledgement, allocation and demuxing.

> And which irq enable/disable/mask/unmask/ack callbacks I need to
> implement for legacy irq, bottom MSI and upper MSI domains?

You need to provide what makes sense for your HW. I would guess that
you need at least mask/unmask and most probably ack at both levels,
and of course a compose_msg callback at the bottom level.

> And where should I add code which globally enable/disable receiving of
> aardvark MSI interrupts? Currently it is part of aardvark driver probe
> function.

Seems like the logical place to put it. The kernel deals with
individual interrupts, and not with global switches.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.