From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hanjun Guo Subject: Re: [PATCH] ACPICA / hwreg: Use acpi_gbl_reduced_hardware to prevent accessing PM registers Date: Sun, 22 Sep 2013 10:50:53 +0800 Message-ID: <523E5B0D.3010104@linaro.org> References: <1379066741-23689-1-git-send-email-hanjun.guo@linaro.org> <94F2FBAB4432B54E8AACC7DFDE6C92E36FEEBC6A@ORSMSX103.amr.corp.intel.com> <94F2FBAB4432B54E8AACC7DFDE6C92E36FEEC15B@ORSMSX103.amr.corp.intel.com> <52366F91.30204@linaro.org> <94F2FBAB4432B54E8AACC7DFDE6C92E36FEEC56A@ORSMSX103.amr.corp.intel.com> <523972F4.9070703@linaro.org> <94F2FBAB4432B54E8AACC7DFDE6C92E36FEFA437@ORSMSX102.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pa0-f54.google.com ([209.85.220.54]:49008 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752596Ab3IVCxN (ORCPT ); Sat, 21 Sep 2013 22:53:13 -0400 Received: by mail-pa0-f54.google.com with SMTP id kx10so2218186pab.13 for ; Sat, 21 Sep 2013 19:53:12 -0700 (PDT) In-Reply-To: <94F2FBAB4432B54E8AACC7DFDE6C92E36FEFA437@ORSMSX102.amr.corp.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Moore, Robert" , "'Rafael J. Wysocki'" Cc: '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'" 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 >