On Sun, 24 Feb 2019 at 15:08, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>
> 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!
>
The mapping of legacy PCIe INTx interrupts onto wired system
interrupts is a property of the PCIe host controller, not of a
particular PCIe device. So I would argue that the code is broken here
as well: it should never attempt to interpret 'interrupt' properties
at the PCI device level as having any bearing on how legacy interrupts
are routed.
> The net effect of the above is that Linux tries to do something vaguely
> sensible, and uses the same interrupt for both the wake-up widget and the
> PCI device. This doesn't work for two reasons: (1) the wake-up widget grabs
> the interrupt in exclusive mode, and (2) the PCI interrupt is still routed
> to the RC, leading to a screaming interrupt. This simply cannot work.
>
> To sort out this mess, we need to lift the confusion between the two
> interrupts. This is done by extending the DT binding to allow the wake-up
> interrupt to be described in a 'wake-up' subnode, sidestepping the issue
> completely. On my Chromebook, it now looks like this:
>
> &pci_rootport {
> mvl_wifi: wifi@0,0 {
> compatible = "pci1b4b,2b42";
> reg = <0x83010000 0x0 0x00000000 0x0 0x00100000
> 0x83010000 0x0 0x00100000 0x0 0x00100000>;
> pinctrl-names = "default";
> pinctrl-0 = <&wlan_host_wake_l>;
> wake-up {
> interrupt-parent = <&gpio0>;
> interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
> wakeup-source;
> };
> };
> };
>
> The driver is then updated to look for this subnode first, and fallback to
> the original, broken behaviour (spitting out a warning in the offending
> configuration).
>
> For good measure, there are two additional patches:
>
> - The wake-up interrupt requesting is horribly racy, and could lead to
> unpredictable behaviours. Let's fix that properly.
>
> - A final patch implementing the above transformation for the whole
> RK3399-based Chromebook range, which all use the same broken
> configuration.
>
> With all that, I finally have PCI legacy interrupts working with the mwifiex
> driver on my Chromebook.
>
> [1] http://www.devicetree.org/open-firmware/bindings/pci/pci2_1.pdf
>
> Marc Zyngier (4):
> dt-bindings/marvell-8xxx: Allow wake-up interrupt to be placed in a
> separate node
> mwifiex: Fetch wake-up interrupt from 'wake-up' subnode when it exists
> mwifiex: Flag wake-up interrupt as IRQ_NOAUTOEN rather than disabling
> it too late
> arm64: dts: rockchip: gru: Move wifi wake-up interrupt into its own
> subnode
>
> .../bindings/net/wireless/marvell-8xxx.txt | 23 ++++++++++++++++++-
> .../dts/rockchip/rk3399-gru-chromebook.dtsi | 8 ++++---
> drivers/net/wireless/marvell/mwifiex/main.c | 13 +++++++++--
> 3 files changed, 38 insertions(+), 6 deletions(-)
>
> --
> 2.20.1
>
>
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