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: <CAJZ5v0gF6JZ8uVNMnro0bdD0g+QMoTeEzB99j6RcKUt3LjmiXw@mail.gmail.com>
Date:	Tue, 30 Jun 2015 20:25:34 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Al Stone <ahs3@...hat.com>
Cc:	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 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?

Rafael
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