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From:   Saravana Kannan <saravanak@google.com>
Date:   Fri, 5 Feb 2021 09:55:08 -0800
Message-ID: <CAGETcx93cee=aH+cOyf-xmYGSHcn6AfBHC=fOw7By6=8JzT56Q@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] of: property: Add fw_devlink support for interrupts
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-tegra <linux-tegra@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Jon Hunter <jonathanh@nvidia.com>,
        Marc Zyngier <maz@kernel.org>,
        Kevin Hilman <khilman@baylibre.com>,
        Android Kernel Team <kernel-team@android.com>,
        Rob Herring <robh@kernel.org>,
        Thierry Reding <treding@nvidia.com>
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On Fri, Feb 5, 2021 at 9:52 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Saravana,
>
> On Fri, Feb 5, 2021 at 6:20 PM Saravana Kannan <saravanak@google.com> wrote:
> > On Fri, Feb 5, 2021 at 2:20 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Fri, Feb 5, 2021 at 11:06 AM Saravana Kannan <saravanak@google.com> wrote:
> > > > On Fri, Feb 5, 2021 at 12:06 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > > On Fri, Feb 5, 2021 at 8:38 AM Marek Szyprowski
> > > > > <m.szyprowski@samsung.com> wrote:
> > > > > > On 04.02.2021 22:31, Saravana Kannan wrote:
> > > > > > > On Thu, Feb 4, 2021 at 3:52 AM Marek Szyprowski
> > > > > > > <m.szyprowski@samsung.com> wrote:
> > > > > > >> On 21.01.2021 23:57, Saravana Kannan wrote:
> > > > > > >>> This allows fw_devlink to create device links between consumers of an
> > > > > > >>> interrupt and the supplier of the interrupt.
> > > > > > >>>
> > > > > > >>> Cc: Marc Zyngier <maz@kernel.org>
> > > > > > >>> Cc: Kevin Hilman <khilman@baylibre.com>
> > > > > > >>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > > > > >>> Reviewed-by: Rob Herring <robh@kernel.org>
> > > > > > >>> Reviewed-by: Thierry Reding <treding@nvidia.com>
> > > > > > >>> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> > > > > > >>> Signed-off-by: Saravana Kannan <saravanak@google.com>
> > > > > > >> This patch landed some time ago in linux-next as commit 4104ca776ba3
> > > > > > >> ("of: property: Add fw_devlink support for interrupts"). It breaks MMC
> > > > > > >> host controller operation on ARM Juno R1 board (the mmci@50000 device
> > > > > > >> defined in arch/arm64/boot/dts/arm/juno-motherboard.dtsi). I didn't
> > > > > > > I grepped around and it looks like the final board file is this or
> > > > > > > whatever includes it?
> > > > > > > arch/arm64/boot/dts/arm/juno-base.dtsi
> > > > > > The final board file is arch/arm64/boot/dts/arm/juno-r1.dts
> > > > > > > This patch just finds the interrupt-parent and then tries to use that
> > > > > > > as a supplier if "interrupts" property is listed. But the only
> > > > > > > interrupt parent I can see is:
> > > > > > >          gic: interrupt-controller@2c010000 {
> > > > > > >                  compatible = "arm,gic-400", "arm,cortex-a15-gic";
> > > > > > >
> > > > > > > And the driver uses IRQCHIP_DECLARE() and hence should be pretty much
> > > > > > > a NOP since those suppliers are never devices and are ignored.
> > > > > > > $ git grep "arm,gic-400" -- drivers/
> > > > > > > drivers/irqchip/irq-gic.c:IRQCHIP_DECLARE(gic_400, "arm,gic-400", gic_of_init);
> > > > > > >
> > > > > > > This doesn't make any sense. Am I looking at the right files? Am I
> > > > > > > missing something?
> > > > > >
> > > > > > Okay, I've added displaying a list of deferred devices when mounting
> > > > > > rootfs fails and got following items:
> > > > > >
> > > > > > Deferred devices:
> > > > > > 18000000.ethernet        platform: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 1c050000.mmci    amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 1c1d0000.gpio    amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 2b600000.iommu   platform: probe deferral - wait for supplier
> > > > > > scpi-power-domains
> > > > > > 7ff50000.hdlcd   platform: probe deferral - wait for supplier scpi-clk
> > > > > > 7ff60000.hdlcd   platform: probe deferral - wait for supplier scpi-clk
> > > > > > 1c060000.kmi     amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 1c070000.kmi     amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 1c170000.rtc     amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > 1c0f0000.wdt     amba: probe deferral - supplier
> > > > > > bus@8000000:motherboard-bus not ready
> > > > > > gpio-keys
> > > > > > Kernel panic - not syncing: VFS: Unable to mount root fs on
> > > > > > unknown-block(0,0)
> > > > > >
> > > > > > I don't see the 'bus@8000000:motherboard-bus' on the deferred devices
> > > > > > list, so it looks that device core added a link to something that is not
> > > > > > a platform device...
> > > >
> > > > Probe deferred devices (even platform devices) not showing up in that
> > > > list is not unusual. That's because devices end up on that list only
> > > > after a driver for them is matched and then it fails.
> > > >
> > > > > Lemme guess: bus@8000000 is a simple bus, but it has an
> > > > > interrupt-map, and the devlink code doesn't follow the mapping?
> > > > >
> > > >
> > > > No, what's happening is that (and this is something I just learned)
> > > > that if a parent has an "#interrupt-cells" property, it becomes your
> > > > interrupt parent. In this case, the motherboard-bus (still a platform
> > > > device) is the parent, but it never probes (because it's simple-bus
> > > > and "arm,vexpress,v2p-p1"). But it becomes the interrupt parent. And
> > > > this mmci device is marked as a consumer of this bus (while still a
> > > > grand-child). Yeah, I'm working on patches (multiple rewrites) to take
> > > > care of cases like this.
> > >
> > > One more reason to scrap the different handling of "simple-bus" and
> > > "simple-pm-bus", and use drivers/bus/simple-pm-bus.c, which is a
> > > platform device driver, for both? (like I originally intended ;-)
> >
> > I'm not sure if this will cause more issues since people are used to
> > simple-bus not needing a driver. I'm afraid to open that pandora's
> > box. Maybe last resort if I don't have any other options.
> >
> > But keeping that aside, I'm confused how interrupts are even working
> > if the parent is a DT node with no driver (let alone a device). Any
> > ideas on what's going on or what I'm misunderstanding?
>
> No driver is needed, as the interrupts are just translated by the map,
> and passed to another interrupt controller, which does have a driver.
>
> Cfr. Section 2.4.3 "Interrupt Nexus Properties" in the DeviceTree
> Specification (https://www.devicetree.org/).
>

Yeah, I need to add interrupt-map support. Sigh. Only so many things I
can fix at a time. Let me know if you want to help.

-Saravana