Re: [Qemu-devel] [PATCH v2]booke: timer: Deactivate timer for target_bit above 61

[Scott Wood <scottwood@freescale.com>]

On 06/10/2013 09:26:18 AM, Alexander Graf wrote:
> On 06/10/2013 02:47 PM, Bhushan Bharat-R65777 wrote:
>> 
>>> -----Original Message-----
>>> From: Andreas Färber [mailto:afaerber@suse.de]
>>> Sent: Monday, June 10, 2013 5:43 PM
>>> To: Bhushan Bharat-R65777
>>> Cc: qemu-ppc@nongnu.org; qemu-devel@nongnu.org; agraf@suse.de; Wood  
>>> Scott-
>>> B07421; Bhushan Bharat-R65777
>>> Subject: Re: [Qemu-devel] [PATCH v2]booke: timer: Deactivate timer  
>>> for
>>> target_bit above 61
>>> 
>>> So IIUC we can only allow 63 bits due to signedness, thus a maximum  
>>> of
>>> (1<<  62), thus target_bit<= 61.
>>> 
>>> Any chance at least the comment can be worded to explain that any  
>>> better? Maybe
>>> also use (target-bit + 1>= 63) or period>  INT64_MAX as condition?
>> How about this:
>>      /* QEMU timer supports a maximum timer of INT64_MAX  
>> (0x7fffffff_ffffffff).
>>       * Run booke fit/wdog timer when
>>       * ((1ULL<<  target_bit + 1)<  0x40000000_00000000), i.e  
>> target_bit = 61.
>>       * Also the time with this maximum target_bit (with current  
>> range of
>>       * CPU frequency PowerPC supports) will be many many years. So  
>> it is
>>       * pretty safe to stop the timer above this threshold. */
> 
> How about
> 
>   /* This timeout will take years to trigger. Treat the timer as  
> disabled. */

There should be at least a brief mention that it's because the QEMU  
timer can't handle larger values, with the detailed explanation in the  
changelog.  A better lower bound on the number of years would be nice  
as well (e.g. "hundreds of years").

-Scott