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Subject: Re: [PATCH v2 2/2] of: property: Add fw_devlink support for
 interrupts
To:     Saravana Kannan <saravanak@google.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     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>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <ab39d157-a150-3f34-ec3a-047821f7c2a8@samsung.com>
Date:   Mon, 8 Feb 2021 09:14:11 +0100
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Hi Saravana,

On 06.02.2021 05:32, Saravana Kannan wrote:
> On Fri, Feb 5, 2021 at 9:55 AM Saravana Kannan <saravanak@google.com> wrote:
>> On Fri, Feb 5, 2021 at 9:52 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>> 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://protect2.fireeye.com/v1/url?k=72fff987-2d64c09f-72fe72c8-0cc47a314e9a-fd7dac11a78508f3&q=1&e=c0dbf5ca-130b-4aac-a011-447e82ca1914&u=https%3A%2F%2Fwww.devicetree.org%2F).
>>>
>> 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.
>>
> Marek,
>
> After reading the DT spec and poking at the code, I THINK this code is
> correct. Can you give it a shot? If it works, then I can clean it up,
> roll in interrupts-extended and send a patch.

Yep, this fixes this issue. Fell free to add:

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

> -Saravana
>
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1300,10 +1300,12 @@ static struct device_node
> *parse_gpio_compat(struct device_node *np,
>   static struct device_node *parse_interrupts(struct device_node *np,
>                                              const char *prop_name, int index)
>   {
> -       if (strcmp(prop_name, "interrupts") || index)
> +       struct of_phandle_args sup_args;
> +       if (strcmp(prop_name, "interrupts"))
>                  return NULL;
>
> -       return of_irq_find_parent(np);
> +       return of_irq_parse_one(np, index, &sup_args) ? NULL : sup_args.np;
>   }
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland