Re: [PATCH] wlcore/wl18xx: Add invert-irq OF property for physically inverted IRQ

[Eugeniu Rosca <erosca@de.adit-jv.com>]

Hi,

cc: Linus Walleij

On Tue, Jun 11, 2019 at 10:00:41AM +0100, Marc Zyngier wrote:
> On 11/06/2019 09:45, Geert Uytterhoeven wrote:
> > CC irqchip
> > 
> > Original thread at
> > https://lore.kernel.org/lkml/20190607172958.20745-1-erosca@de.adit-jv.com/
> > 
> > On Mon, Jun 10, 2019 at 10:30 AM Tony Lindgren <tony@atomide.com> wrote:
> >> * Kalle Valo <kvalo@codeaurora.org> [190610 07:01]:
> >>> Eugeniu Rosca <erosca@de.adit-jv.com> writes:
> >>>
> >>>> The wl1837mod datasheet [1] says about the WL_IRQ pin:
> >>>>
> >>>>  ---8<---
> >>>> SDIO available, interrupt out. Active high. [..]
> >>>> Set to rising edge (active high) on powerup.
> >>>>  ---8<---
> >>>>
> >>>> That's the reason of seeing the interrupt configured as:
> >>>>  - IRQ_TYPE_EDGE_RISING on HiKey 960/970
> >>>>  - IRQ_TYPE_LEVEL_HIGH on a number of i.MX6 platforms
> >>>>
> >>>> We assert that all those platforms have the WL_IRQ pin connected
> >>>> to the SoC _directly_ (confirmed on HiKey 970 [2]).
> >>>>
> >>>> That's not the case for R-Car Kingfisher extension target, which carries
> >>>> a WL1837MODGIMOCT IC. There is an SN74LV1T04DBVR inverter present
> >>>> between the WLAN_IRQ pin of the WL18* chip and the SoC, effectively
> >>>> reversing the requirement quoted from [1]. IOW, in Kingfisher DTS
> >>>> configuration we would need to use IRQ_TYPE_EDGE_FALLING or
> >>>> IRQ_TYPE_LEVEL_LOW.
> >>>>
> >>>> Unfortunately, v4.2-rc1 commit bd763482c82ea2 ("wl18xx: wlan_irq:
> >>>> support platform dependent interrupt types") made a special case out
> >>>> of these interrupt types. After this commit, it is impossible to provide
> >>>> an IRQ configuration via DTS which would describe an inverter present
> >>>> between the WL18* chip and the SoC, generating the need for workarounds
> >>>> like [3].
> >>>>
> >>>> Create a boolean OF property, called "invert-irq" to specify that
> >>>> the WLAN_IRQ pin of WL18* is connected to the SoC via an inverter.
> >>>>
> >>>> This solution has been successfully tested on R-Car H3ULCB-KF-M06 using
> >>>> the DTS configuration [4] combined with the "invert-irq" property.
> >>>>
> >>>> [1] http://www.ti.com/lit/ds/symlink/wl1837mod.pdf
> >>>> [2] https://www.96boards.org/documentation/consumer/hikey/hikey970/hardware-docs/
> >>>> [3] https://github.com/CogentEmbedded/meta-rcar/blob/289fbd4f8354/meta-rcar-gen3-adas/recipes-kernel/linux/linux-renesas/0024-wl18xx-do-not-invert-IRQ-on-WLxxxx-side.patch
> >>>> [4] https://patchwork.kernel.org/patch/10895879/
> >>>>     ("arm64: dts: ulcb-kf: Add support for TI WL1837")
> >>>>
> >>>> Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> >>>
> >>> Tony&Eyal, do you agree with this?
> >>
> >> Yeah if there's some hardware between the WLAN device and the SoC
> >> inverting the interrupt, I don't think we have clear a way to deal
> >> with it short of setting up a separate irqchip that does the
> >> translation.
> > 
> > Yeah, inverting the interrupt type in DT works only for simple devices,
> > that don't need configuration.
> > A simple irqchip driver that just inverts the type sounds like a good
> > solution to me. Does something like that already exists?
> 
> We already have plenty of that in the tree, the canonical example
> probably being drivers/irqchip/irq-mtk-sysirq.c. It should be pretty
> easy to turn this driver into something more generic.

I don't think drivers/irqchip/irq-mtk-sysirq.c can serve the
use-case/purpose of this patch. The MTK driver seems to be dealing with
the polarity inversion of on-SoC interrupts which are routed to GiC,
whereas in this patch we are talking about an off-chip interrupt
wired to R-Car GPIO controller.

It looks to me that the nice DTS sketch shared by Linus Walleij in [5]
might come closer to the concept proposed by Geert? FWIW, the
infrastructure/implementation to make this possible is still not ready.

One question to the wlcore/wl18xx maintainers: Why exactly do you give
freedom to users to set the interrupt as LEVEL_LOW/EDGE_FALLING [6]?
Apparently, this:
 - complicates the wl18xx driver, thus increasing the chance for bugs
 - is not supposed to reflect any HW differences between boards using
   LEVEL_LOW/EDGE_FALLING and the boards using LEVEL_HIGH/EDGE_RISING
 - doesn't bring any obvious advantage to the users, who are expected to
   sense the same behavior regardless of the IRQ type set in DTS
 - prevent the users to set IRQ type to LEVEL_LOW/EDGE_FALLING when
   there is an inverter present between WL_IRQ and SoC
 - seems to be not used almost at all, as 99% of mainline DTS set the
   IRQ type to the canonical/NLCP LEVEL_HIGH/EDGE_RISING

[5] https://patchwork.ozlabs.org/patch/1095690/#2167076
  ("[V1,1/2] gpio: make it possible to set active-state on GPIO lines")
 --------------------8<-------------------
 gpio0: gpio {
    compatible = "foo,chip";
    gpio-controller;
    (...)
 };

 inv0: inverter {
     compatible = "inverter";
     gpio-controller;
     gpios = <&gpio0 0 GPIO_ACTIVE_HIGH>;
 };

 consumer {
    compatible = "bar";
    gpios = <&inv0 0 GPIO_ACTIVE_HIGH>;
 };
 --------------------8<-------------------

[6] bd763482c82ea2 ("wl18xx: wlan_irq: support platform dependent interrupt types")

-- 
Best Regards,
Eugeniu.