Hi Bob,
Sorry for the late reply, I had being on holiday last few days.
On 2013-9-18 23:09, Moore, Robert wrote:
-----Original Message----- From: Hanjun Guo [mailto:hanjun.guo@linaro.org] Sent: Wednesday, September 18, 2013 2:32 AM To: Moore, Robert Cc: 'Rafael J. Wysocki'; 'Len Brown'; Box, David E; 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
On 2013-9-17 1:26, Moore, Robert wrote:
- #define ACPI_REDUCED_HARDWARE TRUE
The intent of this feature is of course, to remove all code that is not
needed -- specifically for hardware-reduced machines where the size of the kernel is important.
On a larger machine, the hardware-reduced flag should be sufficient.
However, I would think that the host OS would look at this flag and realize that it should not be doing certain ACPI hardware-related things up front, rather than later when it finds out that a write to some ACPI hardware fails because the hardware isn't there.
Do you mean we should change the ACPI device driver instead of changing the ACPICA code? that would be a hard job, because hardware ACPI is used everywhere.
I don't really know the answer to this, but something tells me that bad things may happen when a driver expects the ACPI hardware to be there, and it finds out that it isn't, simply by calling one of the ACPI hardware interfaces.
Or, we could word it this way: if a driver is expecting the ACPI hardware to exist, and we are running on a hardware-reduced platform, why is the driver being loaded in the first place?
ok, that would be a reasonable solution.
Oh, things get complicated now, could some linux experts have comments here please?
BTW, hardware-reduced is not restricted to ARM platforms.
Thanks for reminding, may be some other platforms (not only x86, IA64, ARM) will use ACPI in the future.
Thanks Hanjun