linux-kernel - Re: [PATCH v8 8/8] clk: Add KUnit tests for clks registered with struct clk_parent

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Message-ID: <ba88a29c-f05e-4ca3-82d1-0a634613caee@roeck-us.net>
Date: Fri, 27 Sep 2024 17:08:15 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Shuah Khan <skhan@...uxfoundation.org>, Stephen Boyd <sboyd@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>,
 linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
 patches@...ts.linux.dev, kunit-dev@...glegroups.com,
 linux-kselftest@...r.kernel.org, devicetree@...r.kernel.org,
 Brendan Higgins <brendan.higgins@...ux.dev>, David Gow
 <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Rob Herring <robh@...nel.org>,
 Saravana Kannan <saravanak@...gle.com>, Daniel Latypov
 <dlatypov@...gle.com>, Christian Marangi <ansuelsmth@...il.com>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Maxime Ripard <maxime@...no.tech>,
 Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v8 8/8] clk: Add KUnit tests for clks registered with
 struct clk_parent_data

On 9/27/24 13:45, Shuah Khan wrote:
> On 9/27/24 10:19, Guenter Roeck wrote:
>> Copying devicetree maintainers.
>>
>> On Thu, Sep 26, 2024 at 09:39:38PM -0700, Guenter Roeck wrote:
>>> On Thu, Sep 26, 2024 at 09:14:11PM -0700, Guenter Roeck wrote:
>>>> Hi Stephen,
>>>>
>>>> On Thu, Jul 18, 2024 at 02:05:07PM -0700, Stephen Boyd wrote:
>>>>> Test that clks registered with 'struct clk_parent_data' work as
>>>>> intended and can find their parents.
>>>>>
>>>>
>>>> When testing this on arm64, I see the error below. The error is only
>>>> seen if I boot through efi, i.e., with "-bios QEMU_EFI-aarch64.fd"
>>>> qemu parameter.
>>>>
>>>> Any idea what might cause the problem ?
>>>>
>>> I noticed that the new overlay tests fail as well, also with "path '/' not
>>> found".
>>>
>>> [Maybe] answering my own question: I think the problem may be that there
>>> is no devicetree file and thus no devicetree root when booting through
>>> efi (in other words, of_root is NULL). Would it make sense to skip the
>>> tests in that case ?
>>>
>>
>> The problem is that of_root is not initialized in arm64 boots if ACPI
>> is enabled.
>>
>>  From arch/arm64/kernel/setup.c:setup_arch():
>>
>>     if (acpi_disabled)
>>         unflatten_device_tree();        // initializes of_root
>>
>> ACPI is enabled if the system boots from EFI. This also affects
>> CONFIG_OF_KUNIT_TEST, which explicitly checks if of_root exists and
>> fails the test if it doesn't.
>>
>> I think those tests need to add a check for this condition, or affected
>> machines won't be able to run those unit tests. The obvious solution would
>> be to check if of_root is set, but then the associated test case in
>> CONFIG_OF_KUNIT_TEST would not make sense.
>>
>> Any suggestions ?
>>
> 
> Would it work if these tests check if acpi_disabled and skip if it isn't
> disabled? It might be low overhead condition to check from these tests.
> 
> acpi_disabled is exported:
> 
> arch/arm64/kernel/acpi.c:EXPORT_SYMBOL(acpi_disabled);
> arch/loongarch/kernel/acpi.c:EXPORT_SYMBOL(acpi_disabled);
> arch/riscv/kernel/acpi.c:EXPORT_SYMBOL(acpi_disabled);
> arch/x86/kernel/acpi/boot.c:EXPORT_SYMBOL(acpi_disabled);
> 

I don't think that would work. Looking through the use of acpi_init,
I don't think that of_root is always NULL when acpi_init is false; that
just happens to be the case on arm64 when booting through efi.
However, even arm64 has the following code.

         if (acpi_disabled)
                 psci_dt_init();
         else
                 psci_acpi_init();

While psci_dt_init() doesn't set of_root, it does try to do a devicetree
match. So there must be some other condition where acpi_disabled is set
but of_root is set anyway. I just have not found that code path.

Guenter