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

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Message-ID: <CAJZ5v0hgpMWT312+qrzON4EM0+n23g8X-fCQgUugQKNwz+sLtw@mail.gmail.com>
Date:	Tue, 30 Jun 2015 21:05:49 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Al Stone <ahs3@...hat.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Al Stone <al.stone@...aro.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"lenb@...nel.org" <lenb@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>
Subject: Re: [PATCH v2 0/3] Correct for ACPI 5.1->6.0 spec changes in MADT
 GICC entries

Hi Al,

On Tue, Jun 30, 2015 at 8:39 PM, Al Stone <ahs3@...hat.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@...hat.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.

> 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
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