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MIPS: Octeon: Use non-overflowing arithmetic in sched_clock 

With typical mult and shift values, the calculation for Octeon's sched_clock
overflows when using 64-bit arithmetic.  Use 128-bit calculations instead.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/849/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
David Daney 2010-01-08 14:47:36 -08:00 committed by Ralf Baechle
parent 9b54dc5869
commit 0e8a1d8262
1 changed files with 28 additions and 3 deletions
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31
arch/mips/cavium-octeon/csrc-octeon.c
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@ -52,9 +52,34 @@ static struct clocksource clocksource_mips = {
unsigned long long notrace sched_clock(void)
{
return clocksource_cyc2ns(read_c0_cvmcount(),
clocksource_mips.mult,
clocksource_mips.shift);
/* 64-bit arithmatic can overflow, so use 128-bit. */
#if (__GNUC__ < 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ <= 3))
u64 t1, t2, t3;
unsigned long long rv;
u64 mult = clocksource_mips.mult;
u64 shift = clocksource_mips.shift;
u64 cnt = read_c0_cvmcount();
asm (
"dmultu\t%[cnt],%[mult]\n\t"
"nor\t%[t1],$0,%[shift]\n\t"
"mfhi\t%[t2]\n\t"
"mflo\t%[t3]\n\t"
"dsll\t%[t2],%[t2],1\n\t"
"dsrlv\t%[rv],%[t3],%[shift]\n\t"
"dsllv\t%[t1],%[t2],%[t1]\n\t"
"or\t%[rv],%[t1],%[rv]\n\t"
: [rv] "=&r" (rv), [t1] "=&r" (t1), [t2] "=&r" (t2), [t3] "=&r" (t3)
: [cnt] "r" (cnt), [mult] "r" (mult), [shift] "r" (shift)
: "hi", "lo");
return rv;
#else
/* GCC > 4.3 do it the easy way. */
unsigned int __attribute__((mode(TI))) t;
t = read_c0_cvmcount();
t = t * clocksource_mips.mult;
return (unsigned long long)(t >> clocksource_mips.shift);
#endif
}
void __init plat_time_init(void)