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

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Message-ID: <da260b77-2ecb-4486-90cb-6db456d381ef@linuxfoundation.org>
Date: Sat, 28 Sep 2024 13:27:07 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Guenter Roeck <linux@...ck-us.net>, 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>,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v8 8/8] clk: Add KUnit tests for clks registered with
 struct clk_parent_data

On 9/28/24 11:54, Shuah Khan wrote:
> On 9/28/24 11:31, Guenter Roeck wrote:
>> On 9/27/24 17:08, Guenter Roeck wrote:
>>> 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.
>>>
>>
>> I ended up disabling all affected unit tests for arm64. I'll do the same
>> for other architectures if I encounter the problem there as well.
>>
>> Unfortunately that includes all clock unit tests because the tests requiring
>> devicetree support can not be enabled/disabled separately, but that can't be
>> helped and is still better than "mandatory" failures.
>>
> 

of_root is set in drivers/of/pdt.c when it creates the root node.
This could be a definitive test for kunit tests that depend on
devicetree support.

It is an exported symbol. drivers/of/base.c exports it.

thanks,
-- SHuah