Re: [PATCH v5 18/18] Documentation: ACPI for ARM64

[G Gregory <graeme.gregory@linaro.org>]

On 6 January 2015 at 13:50, Hanjun Guo <hanjun.guo@linaro.org> wrote:
> On 2015年01月06日 19:29, Catalin Marinas wrote:
>>
>> On Tue, Jan 06, 2015 at 11:11:07AM +0000, Hanjun Guo wrote:
>>>
>>> On 2015年01月05日 19:05, Catalin Marinas wrote:
>>>>
>>>> On Sun, Jan 04, 2015 at 09:39:24AM +0000, Hanjun Guo wrote:
>>>>>
>>>>> On 2014年12月25日 01:18, Catalin Marinas wrote:
>>>>> [...]
>>>>>>
>>>>>>
>>>>>> In addition to the above and _DSD requirements/banning, I would also
>>>>>> add
>>>>>> some clear statements around:
>>>>>>
>>>>>> _OSC: only global/published capabilities are allowed. For
>>>>>> device-specific _OSC we need a process or maybe we can ban them
>>>>>> entirely
>>>>>> and rely on _DSD once we clarify the process.
>>>>>>
>>>>>> _OSI: firmware must not check for certain _OSI strings. Here I'm not
>>>>>> sure what we would have to do for ARM Linux. Reporting "Windows" does
>>>>>> not make any sense but not reporting anything can, as Matthew Garrett
>>>>>> pointed out, can be interpreted by firmware as "Linux". In addition to
>>>>>> any statements in this document, I suggest you patch
>>>>>> drivers/acpi/acpica/utosi.c accordingly, maybe report "Linux" for ARM
>>>>>> and print a kernel warning so that we notice earlier.
>>>>>>
>>>>>> ACPI_OS_NAME: this is globally defined as "Microsoft Windows NT". It
>>>>>> doesn't make much sense in the ARM context. Could we change it to
>>>>>> "Linux" when CONFIG_ARM64?
>>>
>>>
>>> I think we can introduce a Kconfig such as CONFIG_ACPI_OS_NAME_LINUX,
>>> selected by ARM64 and change ACPI_OS_NAME to "Linux" when
>>> CONFIG_ACPI_OS_NAME_LINUX defined. (we can not add CONFIG_ARM64 in
>>> ACPICA code directly since it will be used by windows too)
>>>
>>> some code like below:
>>
>>
>> This looks fine for me (with some minor comments below) but I'm not an
>> ACPI expert to say there wouldn't be any issues.
>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index b1f9a20..de567a3 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -1,5 +1,6 @@
>>>    config ARM64
>>>           def_bool y
>>> +       select ACPI_OS_NAME_LINUX if ACPI
>>>           select ARCH_BINFMT_ELF_RANDOMIZE_PIE
>>>           select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
>>>           select ARCH_HAS_GCOV_PROFILE_ALL
>>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>>> index 8951cef..11a10ac 100644
>>> --- a/drivers/acpi/Kconfig
>>> +++ b/drivers/acpi/Kconfig
>>> @@ -369,6 +369,10 @@ config ACPI_REDUCED_HARDWARE_ONLY
>>>
>>>             If you are unsure what to do, do not enable this option.
>>>
>>> +config ACPI_OS_NAME_LINUX
>>> +       bool "Using Linux for _OS method" if EXPERT
>>> +       def_bool n
>>
>>
>> No need for a default n, it is off by default. Alternatively you could
>> say:
>>
>>         default y if ARM64
>
>
> ok.
>
>>
>>> +
>>>    source "drivers/acpi/apei/Kconfig"
>>>
>>>    config ACPI_EXTLOG
>>> diff --git a/include/acpi/acconfig.h b/include/acpi/acconfig.h
>>> index 5a0a3e5..db5e13e 100644
>>> --- a/include/acpi/acconfig.h
>>> +++ b/include/acpi/acconfig.h
>>> @@ -69,7 +69,11 @@
>>>     * code that will not execute the _OSI method unless _OS matches the
>>> string
>>>     * below.  Therefore, change this string at your own risk.
>>>     */
>>> +#ifndef ACPI_OS_NAME_USING_LINUX
>>>    #define ACPI_OS_NAME                    "Microsoft Windows NT"
>>> +#else
>>> +#define ACPI_OS_NAME                    "Linux"
>>> +#endif
>>
>>
>> Can you not use CONFIG_ACPI_OS_NAME_LINUX directly here without
>> introducing another macro?
>
>
> acconfig.h is part of ACPICA core and will be shared by windows and
> other OS, so use CONFIG from Linux in this file is not allowed I think.
>

We could just propse
#ifndef ACPI_OS_NAME
#define ACPI_OS_NAME "Microsoft Windows NT"
#endif

to acpica maintainers. This will not alter Windows or other software usage
but we can then override it in Linux when/if we want to.

Graeme