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SubjectRe: [PATCH 2/2] x86 platform driver: intelligent power sharing driver
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.

> > + 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?

-andy


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