Re: [PATCH 3/4] Watchdog exit handling support

[Scott Wood <scottwood@freescale.com>]

On 07/04/2012 06:13 AM, Bhushan Bharat-R65777 wrote:
> 
> 
>> -----Original Message-----
>> From: Wood Scott-B07421
>> Sent: Friday, June 29, 2012 3:57 AM
>> To: Bhushan Bharat-R65777
>> Cc: qemu-ppc@nongnu.org; kvm-ppc@vger.kernel.org; agraf@suse.de; Bhushan Bharat-
>> R65777
>> Subject: Re: [PATCH 3/4] Watchdog exit handling support
>>
>> On 06/28/2012 12:39 AM, Bharat Bhushan wrote:
>>> This patch adds the support to handle the exit caused by watchdog
>>> (KVM_EXIT_WDT). In the handling we clear the TSR register.
>>
>> I'm not sure what the logical split is between this patch and 4/4...
> 
> Ok I will merge 3/4 and 4/4.
> 
>>
>>> diff --git a/hw/ppc_booke.c b/hw/ppc_booke.c index 837a5b6..a9fba15
>>> 100644
>>> --- a/hw/ppc_booke.c
>>> +++ b/hw/ppc_booke.c
>>> @@ -203,6 +203,11 @@ static void booke_wdt_cb(void *opaque)
>>>                               booke_timer->wdt_timer);  }
>>>
>>> +void ppc_booke_wdt_clear_tsr(CPUPPCState *env, target_ulong tsr) {
>>> +    env->spr[SPR_BOOKE_TSR] = tsr & ~(TSR_ENW | TSR_WIS |
>>> +TSR_WRS_MASK); }
>>> +
>>
>> We should probably call this function before returning to KVM, at least after we
>> halt for debug, possibly other times.
> 
> Why clearing watchdog related bits in TSR? This will just reset the
> watchdog state machine. Do we actually want to reset the state
> machine or want watchdog interrupt to not occur when exiting to KVM
> for debug.

We want to prevent long delays in QEMU (especially for debug halt) from
causing watchdog actions (interrupt, reset, etc).  Resetting the state
machine seems like the way to do that.

> Does possibly other times mean except KVM_RUN? 

Not sure what you mean here.  Don't we always use KVM_RUN to enter the
guest?  My point was we definitely want this after we had the guest
halted, and we may want to consider doing it for some other heavyweight
exits.

-Scott