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SubjectRe: [PATCH 2/2] x86 platform driver: intelligent power sharing driver
On Sat, 15 May 2010 01:54:56 -0700
Andy Isaacson <adi@hexapodia.org> wrote:

> On Mon, May 10, 2010 at 10:00:46PM -0400, Andrew Morton wrote:
> > > + int i;
> > > + u16 avg;
> > > +
> > > + for (i = 0; i < IPS_SAMPLE_COUNT; i++)
> > > + total += (u64)(array[i] * 100);
> >
> > Actually, that does work. Somehow the compiler will promote
> > array[i] to u64 _before_ doing the multiplication. I think.
> > Still, it looks like a deliberate attempt to trick the compiler
> > into doing a multiplicative overflow ;)
>
> It seems to promote to int, probably due to the implicit type of
> "100". Aind since array is u16, * 100 can't overflow int. So yes,
> it's safe, but it does catch the eye as potentially unsafe.

Newest version uses do_div, I think I got it right there.

>
> > > + cur_seqno = (thm_readl(THM_ITV) &
> > > ITV_ME_SEQNO_MASK) >>
> > > + ITV_ME_SEQNO_SHIFT;
> > > + if (cur_seqno == last_seqno &&
> > > + time_after(jiffies, seqno_timestamp + HZ)) {
> > > + dev_warn(&ips->dev->dev, "ME failed to
> > > update for more than 1s, likely hung\n");
> > > + } else {
> > > + seqno_timestamp = get_jiffies_64();
> > > + last_seqno = cur_seqno;
> > > + }
> > > +
> > > + last_msecs = jiffies_to_msecs(jiffies);
>
> Once it triggers, this will print the "likely hung" message every
> second until the end of time, won't it?

The ME should eventually reset itself, but in the interim we can't
trust its data. So I should add some better handling for that case
(e.g. disable turbo); however this was more of a debug feature for
early MEs, I don't think it'll happen on production hardware.

Jesse


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