Re: [PATCH] timer: Handle decrements of PIT counter

[Kevin O'Connor]

On Fri, Jun 26, 2020 at 04:09:57PM +0300, Roman Bolshakov wrote:
> On Tue, Jun 23, 2020 at 11:00:24PM -0400, Kevin O'Connor wrote:
> > Good catch.  Could we fix it using the patch below instead though?
> > 
> > -Kevin
> > 
> > 
> > --- a/src/hw/timer.c
> > +++ b/src/hw/timer.c
> > @@ -180,7 +180,7 @@ timer_read(void)
> >      // Read from PIT.
> >      outb(PM_SEL_READBACK | PM_READ_VALUE | PM_READ_COUNTER0, 
> > PORT_PIT_MODE);
> >      u16 v = inb(PORT_PIT_COUNTER0) | (inb(PORT_PIT_COUNTER0) << 8);
> > -    return timer_adjust_bits(v, 0xffff);
> > +    return timer_adjust_bits(-v, 0xffff);
> >  }
> >  
> >  // Return the TSC value that is 'msecs' time in the future.
> 
> Hi Kevin,
> 
> I like the approach much more. Initial count value is 0, PIT rearms the
> timer when 1 is hit, unary negation on unsigned u16 fits perfectly, then
> timer_adjust_bits recieves 0, 1, 2, ... and timer is rearmed at 0xffff.
> 
> Do you want me to send v2 or you plan to apply the fix on your own?

I'm fine with either.

Thanks,
-Kevin