On Thu, Aug 30, 2018 at 08:50:04PM +0200, Marek Behun wrote:
> > > > +static u64 get_counter_value(struct armada_37xx_watchdog *dev)
> > > > +{
> > > > + u64 val;
> > > > +
> > > > + val = readl(dev->reg + CNTR_COUNT_HIGH);
> > > > + val = (val << 32) | readl(dev->reg + CNTR_COUNT_LOW);
> > >
> > > Is this guaranteed to be consistent ? What happens if there is a
> > > 32-bit wrap between those two operations ?
> >
> > hmmm. The address is not divisible by 8, so I can't use readq :( what
> > do you propose?
>
> What do you think of this solution?
>
> u64 val;
> u32 low1, low2;
>
> low1 = readl(dev->reg + CNTR_COUNT_LOW);
> val = readl(dev->reg + CNTR_COUNT_HIGH);
> low2 = readl(dev->reg + CNTR_COUNT_LOW);
>
> /*
> * If low jumped in this short time more than 2^31, a wrap probably
> * occured. Read high again.
> */
> if (low2 - low1 > 0x80000000)
> val = readl(dev->reg + CNTR_COUNT_HIGH);
> val = (val << 32) | low2;
Yes, that is one option. The other would be to read high again
all the time and repeat reading low if high changed on the second
read of high.
high1 = readl(dev->reg + CNTR_COUNT_HIGH);
low = readl(dev->reg + CNTR_COUNT_LOW);
high2 = readl(dev->reg + CNTR_COUNT_HIGH);
if (high2 != high1)
low = readl(dev->reg + CNTR_COUNT_LOW);
val = (high2 << 32) | low;
There is no ambiguity in this case: We _know_ that
a wrap occurred if high1 and high2 are different.
Guenter
