linux-kernel - Re: [PATCH] powernv:idle: Clear r12 on wakeup from stop lite

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Message-ID: <87vangb8cq.fsf@concordia.ellerman.id.au>
Date:   Wed, 28 Jun 2017 22:32:53 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nicholas Piggin <npiggin@...il.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ego@...ux.vnet.ibm.com
Subject: Re: [PATCH] powernv:idle: Clear r12 on wakeup from stop lite

Nicholas Piggin <npiggin@...il.com> writes:

> On Wed, 28 Jun 2017 06:46:49 +0530
> Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com> wrote:
>
>> pnv_wakeup_noloss expects R12 to contain SRR1 value to determine if
>> the wakeup reason is an HMI in CHECK_HMI_INTERRUPT.
>> 
>> When we wakeup with ESL=0, SRR1 will not contain the wakeup reason, so
>> there is no point setting R12 to SRR1.
>> 
>> However, we don't set R12 at all and R12 contains garbage, and still
>> being used to check HMI assuming that it had SRR1. causing the
>> OPAL msglog to be filled with the following print:
>> 	HMI: Received HMI interrupt: HMER = 0x0040000000000000
>> 
>> This patch clears R12 after waking up from stop with ESL=EC=0, so that
>> we don't accidentally enter the HMI handler in pnv_wakeup_noloss if
>> the R12[42:45] corresponds to HMI as wakeup reason.
>> 
>> Bug existed prior to "commit 9d29250136f6 ("powerpc/64s/idle: Avoid SRR
>> usage in idle sleep/wake paths")  but was never hit in practice
>> 
>> Signed-off-by: Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
>> Fixes: 9d29250136f6 ("powerpc/64s/idle: Avoid SRR usage in idle
>> sleep/wake paths")
>
> Thanks guys, appreciate you finding and fixing my bug :)
>
> I think this looks like the best fix. Really minor nitpick but you
> could adjust the line widths on the comment slightly (mpe might do
> that when merging).

You know me too well :}

cheers