From: Michael Ellerman <mpe@ellerman•id.au>
To: "Rafael J. Wysocki" <rafael@kernel•org>,
"Gautham R. Shenoy" <ego@linux•vnet.ibm.com>
Cc: Shilpasri G Bhat <shilpa.bhat@linux•vnet.ibm.com>,
Viresh Kumar <viresh.kumar@linaro•org>,
"Rafael J. Wysocki" <rjw@rjwysocki•net>,
huntbag@linux•vnet.ibm.com, akshay.adiga@linux•vnet.ibm.com,
Vaidyanathan Srinivasan <svaidy@linux•vnet.ibm.com>,
Linux PM <linux-pm@vger•kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
linuxppc-dev <linuxppc-dev@lists•ozlabs.org>,
Stable <stable@vger•kernel.org>
Subject: Re: [v2 PATCH] cpufreq: powernv: Correctly parse the sign of pstates on POWER8 vs POWER9
Date: Fri, 08 Dec 2017 22:47:38 +1100 [thread overview]
Message-ID: <87indhh25h.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <CAJZ5v0jzh1B_8FYciWhpJZVPZNzm3n30NEE25LO_YJ17Wi+h+w@mail.gmail.com>
"Rafael J. Wysocki" <rafael@kernel•org> writes:
> On Thu, Dec 7, 2017 at 6:59 AM, Gautham R. Shenoy
> <ego@linux•vnet.ibm.com> wrote:
>> From: "Gautham R. Shenoy" <ego@linux•vnet.ibm.com>
>>
>> On POWERNV platform, Pstates are 8-bit values. On POWER8 they are
>> negatively numbered while on POWER9 they are positively
>> numbered. Thus, on POWER9, the maximum number of pstates could be as
>> high as 256.
>>
>> The current code interprets pstates as a signed 8-bit value. This
>> causes a problem on POWER9 platforms which have more than 128 pstates.
>> On such systems, on a CPU that is in a lower pstate whose number is
>> greater than 128, querying the current pstate returns a "pstate X is
>> out of bound" error message and the current pstate is reported as the
>> nominal pstate.
>>
>> This patch fixes the aforementioned issue by correctly differentiating
>> the sign whenever a pstate value read, depending on whether the
>> pstates are positively numbered or negatively numbered.
>>
>> Fixes: commit 09ca4c9b5958 ("cpufreq: powernv: Replacing pstate_id with frequency table index")
>> Cc: <stable@vger•kernel.org> #v4.8
>> Signed-off-by: Gautham R. Shenoy <ego@linux•vnet.ibm.com>
>> Tested-and-reviewed-by: Shilpasri G Bhat <shilpa.bhat@linux•vnet.ibm.com>
>> Acked-by: Viresh Kumar <viresh.kumar@linaro•org>
>
> I'm going to apply this, or please let me know if you want to route it
> differently.
Do you mind waiting for now, we're still debating how to fix it.
cheers
next prev parent reply other threads:[~2017-12-08 11:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-07 5:59 [v2 PATCH] cpufreq: powernv: Correctly parse the sign of pstates on POWER8 vs POWER9 Gautham R. Shenoy
2017-12-07 21:25 ` Rafael J. Wysocki
2017-12-08 11:47 ` Michael Ellerman [this message]
2017-12-08 14:08 ` Rafael J. Wysocki
2017-12-08 3:44 ` Balbir Singh
2017-12-11 5:24 ` Gautham R Shenoy
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