linux-kernel - Re: [PATCH v5] clocksource: arch_timer: Fix code to use physical timers when requested

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Message-ID: <20141205073000.GE29274@quad.lixom.net>
Date:	Thu, 4 Dec 2014 23:30:00 -0800
From:	Olof Johansson <olof@...om.net>
To:	Sonny Rao <sonnyrao@...omium.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dianders@...omium.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Marc Zyngier <marc.zyngier@....com>, stable@...r.kernel.org
Subject: Re: [PATCH v5] clocksource: arch_timer: Fix code to use physical
 timers when requested

On Sun, Nov 23, 2014 at 11:02:44PM -0800, Sonny Rao wrote:
> This is a bug fix for using physical arch timers when
> the arch_timer_use_virtual boolean is false.  It restores the
> arch_counter_get_cntpct() function after removal in
> 
> 0d651e4e "clocksource: arch_timer: use virtual counters"
> 
> We need this on certain ARMv7 systems which are architected like this:
> 
> * The firmware doesn't know and doesn't care about hypervisor mode and
>   we don't want to add the complexity of hypervisor there.
> 
> * The firmware isn't involved in SMP bringup or resume.
> 
> * The ARCH timer come up with an uninitialized offset between the
>   virtual and physical counters.  Each core gets a different random
>   offset.
> 
> * The device boots in "Secure SVC" mode.
> 
> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
>   CNTHCTL.PL1PCTEN (both default to 1 at reset)
> 
> One example of such as system is RK3288 where it is much simpler to
> use the physical counter since there's nobody managing the offset and
> each time a core goes down and comes back up it will get reinitialized
> to some other random value.
> 
> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
> Acked-by: Olof Johansson <olof@...om.net>

Applied to a topic branch in arm-soc so we can include it in next/dt and
next/drivers as appropriate for rk3288.


Thanks, all!


-Olof
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