From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Wed, 20 May 2015 21:14:38 +0100
Subject: schedule_timeout sleeps too long after dividing CPU frequency
In-Reply-To: <555CE1B8.70205@free.fr>
References: <20150514144239.GZ2067@n2100.arm.linux.org.uk>
 <20150518115452.GV2067@n2100.arm.linux.org.uk>
 <555CB499.7060600@free.fr> <12867692.bB1EJHiPzq@wuerfel>
 <555CE1B8.70205@free.fr>
Message-ID: <20150520201438.GW2067@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, May 20, 2015 at 09:34:16PM +0200, Mason wrote:
> On 20/05/2015 20:50, Arnd Bergmann wrote:
> >> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
> >> index 6591e26..300f13a 100644
> >> --- a/arch/arm/kernel/smp_twd.c
> >> +++ b/arch/arm/kernel/smp_twd.c
> >> @@ -295,6 +295,10 @@ static void twd_timer_setup(void)
> >>         clk->name = "local_timer";
> >>         clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
> >>                         CLOCK_EVT_FEAT_C3STOP;
> >> +#ifdef CONFIG_TANGOX
> >> +       /*** Tango does not implement low power modes ***/
> >> +       clk->features &= ~CLOCK_EVT_FEAT_C3STOP;
> >> +#endif
> >>         clk->rating = 350;
> >>         clk->set_mode = twd_set_mode;
> >>         clk->set_next_event = twd_set_next_event;
> > 
> > This will disable the feature on all machines that are configured 
> > in the kernel.
> 
> What do you mean, "disable the feature"?
> 
> My proposed patch doesn't change the default, which is to set
> CLOCK_EVT_FEAT_C3STOP unconditionally for all machines.
> 
> And then only for some platforms (in this case only TANGOX)
> CLOCK_EVT_FEAT_C3STOP is *removed* from the features list.

So we build a kernel containing both tangox and OMAP together, and
OMAP starts misbehaving because CLOCK_EVT_FEAT_C3STOP is no longer
set.  That's a regression caused by your change, even if you didn't
intend for anyone else to enable your option.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.