linux-kernel - Re: [PATCH] PM / OPP: 'UNKNOWN' status of opp-table->shared

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Date:	Thu, 16 Jun 2016 15:55:11 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...eaurora.org>
CC:	<linaro-kernel@...ts.linaro.org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <gnurou@...il.com>,
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] PM / OPP: 'UNKNOWN' status of opp-table->shared

On 06/16/2016 03:33 PM, Viresh Kumar wrote:
> dev_pm_opp_get_sharing_cpus() returns 0 even in the case where the OPP
> core doesn't know if the table is shared or not. It is working for most
> of the platforms, as the OPP table was never created and we returned
> -ENODEV then.
>
> But in case of one of the platforms (Jetson TK1) at least, the situation
> is a bit different. The OPP table is created (somehow) before
> dev_pm_opp_get_sharing_cpus() is called and so we returned 0. The caller
> of this routine treated that as 'CPUs don't share OPPs' and that had bad
> consequences on performance.
>
> Fix this by converting 'shared_opp' to an integer and have an extra
> value when its state in undefined. dev_pm_opp_get_sharing_cpus() returns
> -EINVAL now in that case, so that the caller can handle it accordingly
> (cpufreq-dt considers that as 'all CPUs share the table').
>
> Fixes: 6f707daa3833 ("PM / OPP: Add dev_pm_opp_get_sharing_cpus()")
> Reported-by: Alexandre Courbot <acourbot@...dia.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> Hi Alexandre,
>
> This is untested, can you please confirm if this fixes it for you?

Yep, with this cpufreq_init() takes the fallback path and cpufreq 
behaves as expected thereafter.

Thanks for reacting so quickly! Can this go into 4.7 fixes?

Tested-by: Alexandre Courbot <acourbot@...dia.com>