Re: [BUG]i2c_hid_acpi broken with 4.17.2 on Framework Laptop 13 AMD

[Juergen Gross <jgross@xxxxxxxx>]

On 21.12.23 13:40, Jan Beulich wrote:
> On 20.12.2023 17:34, Sébastien Chaumat wrote:
> > Here are the patches I made to xen and linux kernel
> > Plus dmesg (bare metal,xen) and "xl dmesg"
> So the problem looks to be that pci_xen_initial_domain() results in
> permanent setup of IRQ7, when there only "static" ACPI tables (in
> particular source overrides in MADT) are consulted. The necessary
> settings, however, are known only after _CRS for the device was
> evaluated (and possibly _PRS followed by invocation of _SRS). All of
> this happens before xen_register_gsi() is called. But that function's
> call to xen_register_pirq() is short-circuited by the very first if()
> in xen_register_pirq() when there was an earlier invocation. Hence
> the (wrong) "edge" binding remains in place, as was established by
> the earlier call here.
>
> Jürgen, there's an interesting comment in xen_bind_pirq_gsi_to_irq(),
> right before invoking irq_set_chip_and_handler_name(). Despite what
> the comment says (according to my reading), the fasteoi one is _not_
> used in all cases. Assuming there's a reason for this, it's not clear
> to me whether updating the handler later on is a valid thing to do.
> __irq_set_handler() being even an exported symbol suggests that might
> be an option to use here. Then again merely updating the handler may
> not be sufficient, seeing there are also e.g. IRQD_TRIGGER_MASK and
> IRQD_LEVEL.
I understand the last paragraph of that comment to reason, that in case
pirq_needs_eoi() return true even in case of an edge triggered interrupt,
the outcome is still okay.

I don't think updating the handler later is valid.

> Sébastien, to prove the (still pretty weak) theory that the change in
> handler is all that's needed to make things work in your case, could
> you fiddle with pci_xen_initial_domain() to have it skip IRQ7? (That
> of course won't be a proper solution, but ought to be okay for your
> system.) The main weakness of the theory is that IRQ7 really isn't
> very special in this regard - other PCI IRQs routed to the low 16
> IO-APIC pins ought to have similar issues (from the log, on your
> system this would be at least IRQ6 and IRQ10, except that they happen
> to be edge/low, so fitting the ISA defaults); only IRQ16 and up would
> work okay.
>
> Furthermore it might be interesting to know whether ELCR would give us
> any hint in this case. Sadly depending on where you look,
> applicability of this pair of registers (I/O ports 0x4d0 and 0x4d1)
> to other than EISA systems is claimed true or false. Could you perhaps
> make Xen simply log the values read from those two ports, by e.g.
> inserting
>
>      printk("ELCR: %02x, %02x\n", inb(0x4d0), inb(0x4d1));
>
> in, say, setup_dump_irqs()?
>
> Jürgen, looking at pci_xen_initial_domain(), what's the purpose of
> the loop in the final if()? Can this ever do anything useful when
> the earlier comment suggests nr_legacy_irqs() is zero anyway? Or is
> the comment simply inaccurate in not covering the "no IO-APICs" case?
No, I think the final loop would only do something in case probe_8259A()
is detecting a working PIC (which should not be the case IMHO). Could it
be that there have been Xen versions emulating a PIC?

The call of probe_8259A() is in no way depending on nr_ioapics.


Juergen

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