Message-ID: <f5f1c42d-77c0-48c7-ac52-3d4a3b5c2b47@roeck-us.net>
Date: Sat, 28 Sep 2024 14:32:35 -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 9/28/24 12:27, Shuah Khan wrote:
> 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.
> 

That is not always the case, including arm64. It is primarily set in
unflatten_devicetree(), which is not called on arm64 unless acpi_is disabled
(see above).

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

Yes, checking if of_root is NULL and skipping the test in that case might help,
but then there is the of_dtb_root_node_populates_of_root unit test which
explicitly fails if of_root is NULL. The comment describing the test is

/*
  * Test that the 'of_root' global variable is always populated when DT code is
  * enabled. Remove this test once of_root is removed from global access.
  */

The devicetree unit test code explicitly assumes that of_root is set if
CONFIG_OF_EARLY_FLATTREE is enabled, but that is not always the case
(again, of_root is NULL on arm64 unless acpi is disabled).

Guenter

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