Re: [PATCH v2 2/2] of: property: Add fw_devlink support for interrupts

[Saravana Kannan]

On Fri, Feb 5, 2021 at 2:20 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Saravana,
>
> On Fri, Feb 5, 2021 at 11:06 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> > On Fri, Feb 5, 2021 at 12:06 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > > On Fri, Feb 5, 2021 at 8:38 AM Marek Szyprowski
> > > <m.szyprowski@xxxxxxxxxxx> wrote:
> > > > On 04.02.2021 22:31, Saravana Kannan wrote:
> > > > > On Thu, Feb 4, 2021 at 3:52 AM Marek Szyprowski
> > > > > <m.szyprowski@xxxxxxxxxxx> 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@xxxxxxxxxx>
> > > > >>> Cc: Kevin Hilman <khilman@xxxxxxxxxxxx>
> > > > >>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > > >>> Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
> > > > >>> Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
> > > > >>> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > > > >>> Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> > > > >> 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?

-Saravana