Re: [PATCH] ACPICA / hwreg: Use acpi_gbl_reduced_hardware to prevent accessing PM registers

[Hanjun Guo <hanjun.guo@linaro.org>]

On 2013-9-14 4:16, Moore, Robert wrote:
> 
> 
>> -----Original Message-----
>> From: Moore, Robert
>> Sent: Friday, September 13, 2013 6:08 AM
>> To: Hanjun Guo; Rafael J. Wysocki; Len Brown
>> Cc: Zheng, Lv; linux-acpi@vger.kernel.org; patches@linaro.org; linaro-
>> kernel@lists.linaro.org; linaro-acpi@lists.linaro.org
>> Subject: RE: [PATCH] ACPICA / hwreg: Use acpi_gbl_reduced_hardware to
>> prevent accessing PM registers
>>
>> NOT_IMPLEMENTED refers to the software only; therefore AE_SUPPORT should
>> be returned.
>>
>> Otherwise, seems like this may be a good idea.
> 
> 
> On the other hand, could one not argue that the host OS should darn well know that
> it is executing on a hardware-reduced platform and not call these functions in the
> first place?

Well, there is a macro ACPI_REDUCED_HARDWARE and used to switch off the
compiling of these functions on hardware-reduced platform, if
ACPI_REDUCED_HARDWARE is TRUE, those functions will never be called.

But is that reasonable? When somebody want to use the ACPI code on
hardware-reduced platform, they should introduce a patch just like:

- #define ACPI_REDUCED_HARDWARE           FALSE
+ #define ACPI_REDUCED_HARDWARE           TRUE
in include/acpi/acconfig.h

and this patch does not exist in upstream, and it will never be accepted by
upstream too, it is weird. so we should proposal another way.

I thought about introducing a kernel config such as CONFIG_ACPI_REDUCED_HARDWARE
to enable ACPI_REDUCED_HARDWARE, but it is just the same as a macro, and I drop
it.

So, this is a problem should be solved for hardware-reduced platform, use falg
acpi_gbl_reduced_hardware seems a good solution.

Thanks
Hanjun

> 
> Bob