[PATCH v2 0/3] Correct for ACPI 5.1->6.0 spec changes in MADT GICC entries

[Rafael J. Wysocki]

Hi Al,

On Tue, Jun 30, 2015 at 7:29 PM, Al Stone <ahs3 at redhat.com> wrote:
> On 06/30/2015 11:07 AM, Sudeep Holla wrote:
>> Hi Al,
>>
>> On 18/06/15 23:36, Al Stone wrote:
>>> In the ACPI 5.1 version of the spec, the struct for the GICC subtable
>>> (struct acpi_madt_generic_interrupt) of the MADT is 76 bytes long; in
>>> ACPI 6.0, the struct is 80 bytes long.  But, there is only one definition
>>> in ACPICA for this struct -- and that is the 6.0 version.  Hence, when
>>> BAD_MADT_ENTRY() compares the struct size to the length in the GICC
>>> subtable, it fails if 5.1 structs are in use, and there are systems in
>>> the wild that have them.
>>>
>>> Note that this was found in linux-next and these patches apply against
>>> that tree and the arm64 kernel tree; 4.1-rc8 does not appear to have this
>>> problem since it still has the 5.1 struct definition.
>>>
>>> Even though there is precendent in ia64 code for ignoring the changes in
>>> size, this patch set instead tries to verify correctness.  The first patch
>>> in the set adds macros for easily using the ACPI spec version.  The second
>>> patch adds the BAD_MADT_GICC_ENTRY() macro that uses the version macros to
>>> check the GICC subtable only, accounting for the difference in specification
>>> versions that are possible.  The final patch replaces BAD_MADT_ENTRY usage
>>> with the BAD_MADT_GICC_ENTRY macro in arm64 code, which is currently the
>>> only architecture affected.  The BAD_MADT_ENTRY() will continue to work as
>>> is for all other MADT subtables.
>>>
>>
>> We need to get this series or a patch to remove the check(similar to
>> ia64) based on what Rafael prefers. Without that, platforms using ACPI
>> on ARM64 fails to boot with latest mainline. This blocks any testing on
>> ARM64/ACPI systems.
>>
>> Regards,
>> Sudeep
>
> I have not received any other feedback than some Reviewed-bys from
> Hanjun and an ACK from Will for the arm64 patch.
>
> And absolutely agreed: this is a blocker for arm64/ACPI, starting with
> the ACPICA 20150515 patches which appear to have gone in with 4.2-rc1.
>
> Rafael?  Ping?

I overlooked the fact that this was needed to fix a recent regression,
sorry about that.

Actually, if your patch fixes an error introduced by a specific
commit, it is good to use the Fixes: tag to indicate that.  Which I
still would like to do, so which commit is fixed by this?

> Do we need these to go through your tree or the arm64
> tree?  Without this series (or an ia64-like solution), we have ACPI
> systems in the field that cannot boot.

I'm not quite sure why the definition of BAD_MADT_GICC_ENTRY has to go
into include/linux/acpi.h.  Why is it necessary in there?

Rafael