Date: Thu, 20 Nov 2014 09:49:00 +0100
From: Maxime Ripard <maxime.ripard@free-electrons.com>
To: Sonny Rao <sonnyrao@chromium.org>
Cc: linux-arm-kernel@lists.infradead.org, Mark Rutland <Mark.Rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Russell King <linux@arm.linux.org.uk>,
        Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, dianders@chromium.org,
        Marc Zyngier <marc.zyngier@arm.com>,
        Sudeep Holla <Sudeep.Holla@arm.com>, Olof Johansson <olof@lixom.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@codeaurora.org>
Subject: Re: [PATCH v4] clocksource: arch_timer: Fix code to use physical
 timers when requested
Message-ID: <20141120084900.GC24143@lukather>
References: <1412753937-29343-1-git-send-email-sonnyrao@chromium.org>
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Hi,

On Wed, Oct 08, 2014 at 12:38:57AM -0700, 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
>=20
> 0d651e4e "clocksource: arch_timer: use virtual counters"
>=20
> We need this on certain ARMv7 systems which are architected like this:
>=20
> * The firmware doesn't know and doesn't care about hypervisor mode and
>   we don't want to add the complexity of hypervisor there.
>=20
> * The firmware isn't involved in SMP bringup or resume.
>=20
> * The ARCH timer come up with an uninitialized offset between the
>   virtual and physical counters.  Each core gets a different random
>   offset.
>=20
> * The device boots in "Secure SVC" mode.
>=20
> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
>   CNTHCTL.PL1PCTEN (both default to 1 at reset)
>=20
> 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.
>=20
> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
> Acked-by: Olof Johansson <olof@lixom.net>

Has this been merged yet?

If not, you can add my Tested-by, it makes the Allwinner A31 boot
flawlessly with the arch timers (together with the patch "clocksource:
arch_timer: Allow the device tree to specify uninitialized timer
registers")

Thanks!
Maxime

Maxime

--=20
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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