On 06/09/2015 12:16 AM, Zheng, Lv wrote:
> Hi,
> 
> The patch is wrong.
> If we want to dump tables without accessing /dev/mem, we have acpidump -c.
> The only problem here is:
> There is a bug that even with -c specified, acpidump cannot work without accessing /dev/mem.
> So we shouldn't introduce a new portable acpidump OSL but should fix the very problem.
> 
> We've noticed the similar issue in handling this kernel bug:
> https://bugzilla.kernel.org/show_bug.cgi?id=87971
> The fix for this issue can be found here:
> https://github.com/acpica/acpica/pull/77
> 
> Thanks and best regards
> -Lv

The problem I have with this fix for the issue is that this command:

	# acpidump -n APIC

will work on x86 but fail on arm64.  Getting the -c option to work properly
is a good thing, and should be done regardless.  But, this means we have to
use "acpidump -c -n APIC" on systems without /dev/mem.  For my part:

   (a) these are not really customized tables, but the standard ACPI tables
       used to boot the system, so using -c is a little confusing, and

   (b) we now have to use different commands on different architectures to
       get the same result.

My preference would be that the same command has the same behavior everywhere,
which is why I patched it the way I did.

This happens to be very useful on arm64 where /dev/mem is not reliable, but it
could also be usable on any system that does not want to expose /dev/mem for
some reason.  I think the advantage of the patch sent is that the user command
stays the same no matter what the situation.

>> From: Devel [mailto:devel-bounces(a)acpica.org] On Behalf Of Al Stone
>> Sent: Thursday, June 04, 2015 8:43 AM
>>
>> On arm64 systems in particular, the use of /dev/mem is not recommended.  The
>> contents may or may not be valid depending on the memory map being used, since
>> they are not standardized.
>>
>> The attached patch will cause arm64 (aka ARMv8 or AArch64) Linux systems to
>> use a new file called source/os_specific/service_layers/oslinuxtbl_nodevmem.c
>> (a subset of the oslinuxtbl.c code) that allows acpidump to read all ACPI
>> tables from /sys/firmware/acpi instead of from /dev/mem.  This will help ensure
>> that the tables retrieved are the ones actually being used and that their
>> content is correct.
>>
>> This patch applies on top of the 20150515 version, and I have included it in
>> the 20150515-2 versions of the Fedora and Debian packages.  I've tried the
>> resulting acpidump on x86, x86_64 and arm64 systems and it seems to work well.
>>
>> Signed-off-by: Al Stone <ahs3(a)redhat.com>
>>
>> --
>> ciao,
>> al
>> -----------------------------------
>> Al Stone
>> Software Engineer
>> Red Hat, Inc.
>> ahs3(a)redhat.com
>> -----------------------------------


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