[PATCH] ARM: smp_twd: make sure timer is stopped before registering it

[Shilimkar, Santosh]

On Fri, Dec 23, 2011 at 4:09 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> On 23/12/11 06:41, Shilimkar, Santosh wrote:
>> On Thu, Dec 22, 2011 at 8:01 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
>>> On secondary CPUs, the Timer Control Register is not reset
>>> to a sane value before the timer is registered, and the TRM
>>> doesn't seem to indicate any reset value either. In some cases,
>>> the kernel will take an interrupt too early, depending on what
>>> junk was present in the registers at reset time.
>>>
>>> The fix is to set the Timer Control Register to 0 before
>>> registering the clock_event_device and enabling the interrupt.
>>>
>>> Problem seen on VE (Cortex A5) and Tegra.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
>>> ---
>>>  arch/arm/kernel/smp_twd.c |    2 ++
>>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
>>> index a8a6682..2442bbb 100644
>>> --- a/arch/arm/kernel/smp_twd.c
>>> +++ b/arch/arm/kernel/smp_twd.c
>>> @@ -167,6 +167,8 @@ void __cpuinit twd_timer_setup(struct clock_event_device *clk)
>>>
>>>        twd_calibrate_rate();
>>>
>>> +       __raw_writel(0, twd_base + TWD_TIMER_CONTROL);
>>> +
>> Is it because of junk value in register or something programmed as part of the
>> calibrate function. I suspect it might be because of what's getting programmed
>> as part of calibrate function.
>
> The calibration only affects the boot CPU, and is what puts it in a
> known state (the timer is counting, but interrupts are disabled at the
> timer level, making it safe to enable interrupts at the GIC level).
>
> This problem only affects the secondary CPUs, which are in an unknown
> state when we enable the interrupt.
>
I see now. Thanks

Regards
Santosh