Messages in this thread | | | Date | Tue, 5 Nov 2002 13:57:16 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: [PATCH] Re: time() glitch on 2.4.18: solved |
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On Tue, 5 Nov 2002, Jim Paris wrote:
> > BTW, why not trying to resync, with something like : > > > > if (count >= LATCH) > > count = (count >> 8) | inb(0x40) << 8; > > That's best if we really are out of sync, but it's hard to tell. It > could be that the 8253's latch value got clobbered somehow, in which > case we definitely want to fix that or our timer interrupts will come > out at the wrong rate. We also still need to double-check that > count < LATCH after your code. > > Unless we assume that an unpaired read is more common than having the > latch value clobbered in some other way, then I think just resetting > the counter should be okay. Since none of this _should_ ever happen > (but did on my system, grr), it's probably not worth making it too > complicated just to try to figure out what went wrong. > > Updated patch with the printk and corrected conditional is below. > > -jim > > diff -urN linux-2.4.18/arch/i386/kernel/time.c linux-2.4.18-jim/arch/i386/kernel/time.c > --- linux-2.4.18/arch/i386/kernel/time.c Fri Mar 15 18:28:53 2002 > +++ linux-2.4.18-jim/arch/i386/kernel/time.c Tue Nov 5 12:39:38 2002 > @@ -501,6 +501,18 @@ > > count = inb_p(0x40); /* read the latched count */ > count |= inb(0x40) << 8; > + > + /* Any unpaired read will cause the above to swap MSB/LSB > + forever. Try to detect this and reset the counter. */ > + if (count >= LATCH) { > + printk(KERN_WARNING > + "i8253 count too high! resetting..\n"); > + outb_p(0x34, 0x43); > + outb_p(LATCH & 0xff, 0x40); > + outb(LATCH >> 8, 0x40); > + count = LATCH - 1; > + } > + > spin_unlock(&i8253_lock); > > count = ((LATCH-1) - count) * TICK_SIZE; > -
No! You will break many machines. You cannot use out_p() when writing the latch it __must__ be out(). the "_p" puts a write to another port between the two writes. That will screw up the internal state-machine of most PITs including AMD-SC520.
Again, any time you must make two consecutive writes to the same device port to set it, you must not use the "_p" version. The above latch setting must be:
outb(LATCH & 0xff, 0x40); outb(LATCH >> 8, 0x40);
Of course, the second write could have a "_p" option, but you won't need it.
Cheers, Dick Johnson Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips). Bush : The Fourth Reich of America
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