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

Al Stone ahs3 at redhat.com
Tue Jun 30 12:57:14 PDT 2015

On 06/30/2015 01:05 PM, Rafael J. Wysocki wrote:
> Hi Al,
> On Tue, Jun 30, 2015 at 8:39 PM, Al Stone <ahs3 at redhat.com> wrote:
>> On 06/30/2015 12:25 PM, Rafael J. Wysocki wrote:
>>> 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?
>> I only placed it there since it seemed to make sense, and the issue is
>> generic to ACPI, not just ARM.  Granted ARM is the only arch using the
>> GICC subtable in MADT,
> Precisely.
>> but this is fixing how ACPICA implemented the spec,
> So that should be fixed in ACPICA eventually and linux/acpi.h is not
> an ACPICA file even.
> It is possible to apply an ACPICA fix to Linux before it goes to
> upstream ACPICA if it fixes a real problem in Linux.  We've done
> things like that.

Fair enough.  I've been reluctant to add further divergence, personally.

>> which in turn was ambiguous (and an errata is forthcoming to fix that).
>> That being said, though, I'm definitely open to other possibilities.
> So I'd prefer an ACPICA fix and if that's not viable, an ARM-specific
> fix to fill the gap while ACPICA is being updated.
> Thanks,
> Rafael

Hrm.  I'll look into the ACPICA fix.  I'm sure it's possible, but it may
be messy.  I will talk to Bob Moore and Lv Zheng about that, too.  This
sort of thing has surely happened before, though.

In the meantime, I'll put together a new version of this patch that is
ARM-specific to fill the gap.  Using linux/irqchip/arm-gic-acpi.h does
make sense.

Thanks for all the feedback, Rafael.

Al Stone
Software Engineer
Red Hat, Inc.
ahs3 at redhat.com

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