On Wed, 27 Feb 2019 at 11:02, Marc Zyngier [off-list ref] wrote:

+ Lorenzo

Hi Brian,

On 26/02/2019 23:28, Brian Norris wrote:

quoted

+ others

Hi Marc,

Thanks for the series. I have a few bits of history to add to this, and
some comments.

On Sun, Feb 24, 2019 at 02:04:22PM +0000, Marc Zyngier wrote:

quoted

For quite some time, I wondered why the PCI mwifiex device built in my
Chromebook was unable to use the good old legacy interrupts. But as MSIs
were working fine, I never really bothered investigating. I finally had a
look, and the result isn't very pretty.

On this machine (rk3399-based kevin), the wake-up interrupt is described as
such:

&pci_rootport {
     mvl_wifi: wifi@0,0 {
             compatible = "pci1b4b,2b42";
             reg = <0x83010000 0x0 0x00000000 0x0 0x00100000
                    0x83010000 0x0 0x00100000 0x0 0x00100000>;
             interrupt-parent = <&gpio0>;
             interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
             pinctrl-names = "default";
             pinctrl-0 = <&wlan_host_wake_l>;
             wakeup-source;
     };
};

Note how the interrupt is part of the properties directly attached to the
PCI node. And yet, this interrupt has nothing to do with a PCI legacy
interrupt, as it is attached to the wake-up widget that bypasses the PCIe RC
altogether (Yay for the broken design!). This is in total violation of the
IEEE Std 1275-1994 spec[1], which clearly documents that such interrupt
specifiers describe the PCI device interrupts, and must obey the
INT-{A,B,C,D} mapping. Oops!

You're not the first person to notice this. All the motivations are not
necessarily painted clearly in their cover letter, but here are some
previous attempts at solving this problem:

[RFC PATCH v11 0/5] PCI: rockchip: Move PCIe WAKE# handling into pci core
https://lkml.kernel.org/lkml/20171225114742.18920-1-jeffy.chen@rock-chips.com/
http://lkml.kernel.org/lkml/20171226023646.17722-1-jeffy.chen@rock-chips.com/

As you can see by the 12th iteration, it wasn't left unsolved for lack
of trying...

I wasn't aware of this. That's definitely a better approach than my
hack, and I would really like this to be revived.

I don't think this approach is entirely sound either.

From the side of the PCI device, WAKE# is just a GPIO line, and how it
is wired into the system is an entirely separate matter. So I don't
think it is justified to overload the notion of legacy interrupts with
some other pin that may behave in a way that is vaguely similar to how
a true wake-up capable interrupt works.

So I'd argue that we should add an optional 'wake-gpio' DT property
instead to the generic PCI device binding, and leave the interrupt
binding and discovery alone.