Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
x86: Fix serialization in pit_expect_msb()
+22
-7
+22
-7
arch/x86/kernel/tsc.c
+22
-7
arch/x86/kernel/tsc.c
···
275
275
* use the TSC value at the transitions to calculate a pretty
276
276
* good value for the TSC frequencty.
277
277
*/
278
+
static inline int pit_verify_msb(unsigned char val)
279
+
{
280
+
/* Ignore LSB */
281
+
inb(0x42);
282
+
return inb(0x42) == val;
283
+
}
284
+
278
285
static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
279
286
{
280
287
int count;
281
288
u64 tsc = 0;
282
289
283
290
for (count = 0; count < 50000; count++) {
284
-
/* Ignore LSB */
285
-
inb(0x42);
286
-
if (inb(0x42) != val)
291
+
if (!pit_verify_msb(val))
287
292
break;
288
293
tsc = get_cycles();
289
294
}
···
341
336
* to do that is to just read back the 16-bit counter
342
337
* once from the PIT.
343
338
*/
344
-
inb(0x42);
345
-
inb(0x42);
339
+
pit_verify_msb(0);
346
340
347
341
if (pit_expect_msb(0xff, &tsc, &d1)) {
348
342
for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) {
···
352
348
* Iterate until the error is less than 500 ppm
353
349
*/
354
350
delta -= tsc;
355
-
if (d1+d2 < delta >> 11)
356
-
goto success;
351
+
if (d1+d2 >= delta >> 11)
352
+
continue;
353
+
354
+
/*
355
+
* Check the PIT one more time to verify that
356
+
* all TSC reads were stable wrt the PIT.
357
+
*
358
+
* This also guarantees serialization of the
359
+
* last cycle read ('d2') in pit_expect_msb.
360
+
*/
361
+
if (!pit_verify_msb(0xfe - i))
362
+
break;
363
+
goto success;
357
364
}
358
365
}
359
366
printk("Fast TSC calibration failed\n");