Re: [Devel] [PATCH 0/7] Start deprecating _OSI on new architectures

[Al Stone <ahs3 at redhat.com>]

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On 01/23/2015 08:43 AM, Rafael J. Wysocki wrote:
> Hi Al,
> 
> On Thursday, January 22, 2015 05:44:37 PM al.stone(a)linaro.org wrote:
>> From: Al Stone <al.stone(a)linaro.org>
>>
>> The use of the ACPI _OSI method in Linux has a long and sordid history.
>> Instead of perpetuating past complications on new architectures, the 
>> consensus amongst those writing the ACPI specification and those using
>> it seems to be to ultimately deprecate the use of _OSI.  I plan to
>> propose such a change to the ACPI specification in the near future.
>>
>> In the meantime, these patches rearrange the implementation of _OSI so
>> that it can be deprecated, or ultimately removed completely, on at least
>> arm64 platforms.  This is done by simply moving the functions implementing 
>> _OSI to arch-dependent locations.  For x86, there should be no change
>> in functionality.  For ia64, while it does duplicate some code from x86,
>> there is no longer any connection to the ACPI blacklist code that is only
>> used by x86.  For arm64, any use of the _OSI method generates a warning
>> that it has been deprecated, and then always returns false; i.e., that
>> the capability being queried for, whether OS name or functionality, is
>> not supported.  This is the first six of the patches.
> 
> While I seem to understand the motivation, I don't really like moving code
> around, especially in the ia64 area where we have limited means to test the
> changes.  And I hate code duplication pretty much in any form.

I'm not too wild about it either, but it seemed to avoid #ifdefs when I
was trying to think it through.

> Also I don't see anything wrong with sharing code between x86 and ia64 like
> we do today.

Fair enough.  That's entirely up to you; the only reason I saw for
separating them was removing the one call to check the blacklist on
ia64.  That would have a tiny time savings at boot time, but it is
definitely down in the noise level.

> So, why don't you move the _OSI handling out of osl.c into a separate file
> that will only build if something like CONFIG_ARCH_SPECIFIC_ACPI_OSI is not
> set (and same for blacklist.c).  Then, you'll only need to make ARM64
> set CONFIG_ARCH_SPECIFIC_ACPI_OSI and provide the necessary functions
> and you can leave the other architectures alone.
> 
> Does that make sense to you?

It does.  I'll rewrite these based on that approach.  Definitely a lot
less code motion involved...

>> The final patch changes the default value for the _OS_ method for arm64
>> only.  Since there is no need to pretend to be older versions of Windows,
>> or any other OS at all, the _OS_ method will return "Linux" on arm64.
>> One can still use the acpi_os_name kernel parameter if there is a need
>> to use some other value.
>>
>> Since we are breaking apart code previously shared, I have tried to make
>> it so that applying the x86 patches alone will continue to compile, at
>> the expense of breaking the build on non-x86 platforms.  However, once
>> all of the patches are applied, we should be able to compile on all three
>> architectures.  It is best to treat these as one whole.
>>
>> I have only done simple testing with these patches on arm64 and x86 (AMD
>> Seattle and a Lenovo t440s ThinkPad, respectively).  Things seem to work
>> as they should once booted, but this is a very, very small sample of
>> possible machines.  The ia64 patches cross-compile, but I personally have
>> no way to test them.
>>
>> The arm64 patches also rely on having applied Hanjun's patches for ACPI 5.1
>> on arm64 [0].  The x86 and ia64 parts are not dependent on that patch set,
>> though, and should be usable independently (i.e., patches 1, 3, 4 and 6).
>>
>> NB: some of the patches do not pass checkpatch.pl; the failures I saw were
>> all part of the original code but are only showing up because that code is
>> changing location, so I have left them as is.  If necessary, they could be
>> fixed but I was more concerned about the number of changes needed on ia64
>> and not having any way to test them.
>>
>>
>> [0] https://lkml.org/lkml/2015/1/14/586
>>
>>
>> Al Stone (6):
>>   ia64: ACPI: move kernel acpi files to a directory
>>   arm64: ACPI: move kernel acpi files to a directory
>>   x86: ACPI: create arch-dependent version of acpi_osi_handler()
>>   ia64: ACPI: create arch-dependent version of acpi_osi_handler()
>>   arm64: ACPI: create arch-dependent version of acpi_osi_handler()
>>   x86: ia64: arm64: ACPI: move _OSI support functions to arch-dependent
>>     locations
>>
>> Hanjun Guo (1):
>>   ACPI: use Linux as ACPI_OS_NAME for _OS on ARM64
>>
>>  arch/arm64/Kconfig               |    1 +
>>  arch/arm64/kernel/Makefile       |    2 +-
>>  arch/arm64/kernel/acpi.c         |  359 --------------
>>  arch/arm64/kernel/acpi/Makefile  |    1 +
>>  arch/arm64/kernel/acpi/acpi.c    |  359 ++++++++++++++
>>  arch/arm64/kernel/acpi/osi.c     |   26 +
>>  arch/ia64/kernel/Makefile        |    2 +-
>>  arch/ia64/kernel/acpi-ext.c      |  104 ----
>>  arch/ia64/kernel/acpi.c          | 1000 --------------------------------------
>>  arch/ia64/kernel/acpi/Makefile   |    1 +
>>  arch/ia64/kernel/acpi/acpi-ext.c |  104 ++++
>>  arch/ia64/kernel/acpi/acpi.c     | 1000 ++++++++++++++++++++++++++++++++++++++
>>  arch/ia64/kernel/acpi/osi.c      |  119 +++++
>>  arch/x86/kernel/acpi/Makefile    |    2 +-
>>  arch/x86/kernel/acpi/blacklist.c |  327 +++++++++++++
>>  arch/x86/kernel/acpi/boot.c      |    5 +-
>>  arch/x86/kernel/acpi/osi.c       |  255 ++++++++++
>>  drivers/acpi/Kconfig             |    8 +
>>  drivers/acpi/Makefile            |    1 -
>>  drivers/acpi/blacklist.c         |  323 ------------
>>  drivers/acpi/osl.c               |  217 ---------
>>  include/acpi/acconfig.h          |    2 +
>>  include/acpi/platform/aclinux.h  |    4 +
>>  include/linux/acpi.h             |    4 +-
>>  24 files changed, 2215 insertions(+), 2011 deletions(-)
>>  delete mode 100644 arch/arm64/kernel/acpi.c
>>  create mode 100644 arch/arm64/kernel/acpi/Makefile
>>  create mode 100644 arch/arm64/kernel/acpi/acpi.c
>>  create mode 100644 arch/arm64/kernel/acpi/osi.c
>>  delete mode 100644 arch/ia64/kernel/acpi-ext.c
>>  delete mode 100644 arch/ia64/kernel/acpi.c
>>  create mode 100644 arch/ia64/kernel/acpi/Makefile
>>  create mode 100644 arch/ia64/kernel/acpi/acpi-ext.c
>>  create mode 100644 arch/ia64/kernel/acpi/acpi.c
>>  create mode 100644 arch/ia64/kernel/acpi/osi.c
>>  create mode 100644 arch/x86/kernel/acpi/blacklist.c
>>  create mode 100644 arch/x86/kernel/acpi/osi.c
>>  delete mode 100644 drivers/acpi/blacklist.c
>>
>>
> 


-- 
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3(a)redhat.com
-----------------------------------