> -----Original Message-----
> From: Alexander Graf [mailto:ag...@suse.de]
> Sent: Monday, June 10, 2013 11:40 PM
> To: Wood Scott-B07421
> Cc: Bhushan Bharat-R65777; Andreas Färber; qemu-...@nongnu.org; qemu-
> de...@nongnu.org; Wood Scott-B07421
> Subject: Re: [Qemu-devel] [PATCH v2]booke: timer: Deactivate timer for
> target_bit above 61
>
>
> On 10.06.2013, at 19:20, Scott Wood wrote:
>
> > 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:afaer...@suse.de]
> >>>> Sent: Monday, June 10, 2013 5:43 PM
> >>>> To: Bhushan Bharat-R65777
> >>>> Cc: qemu-...@nongnu.org; qemu-devel@nongnu.org; ag...@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,
>
> If it can't handle higher values, maybe it's better to just set the timer
> value
> to INT64_MAX when we detect an overflow? That would make the code plainly
> obvious.
>
What about below comment (a mix of both :)):
/* Timeout calculated with (target_bit + 1) > 62 will take
* hundreds of years to trigger. Treat the timer as disabled.
* Also this timeout is within the qemu supported maximum
* timeout limit (INT64_MAX.). */
-Bharat
>
> Alex
>
> > 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
>
