Current __udelay implementation will cause internal overflow on the first multiplication. Basically, the multiplication is: X = usecs * 2**64 / (100000 / HZ) And maximum input usecs value is 5000 (MAX_UDELAY_MS * 1000). If usecs == 5000 and HZ == 1000, X is 5 * 2**64. Of course this can not be held in 64bit variable. How should we avoid the overflow? 1. Use smaller HZ. HZ < 200 should be OK. 2. Use smaller MAX_UDELAY_MS. The arch specific delay.h can provide its own MAX_UDELAY_MS. MAX_UDELAY_MS == 1 should be OK. 3. Use smaller multiplier. This example should be OK (but lose some precision on larger HZ) #if HZ < (1000 / MAX_UDELAY_MS) usecs *= (0x8000000000000000UL / (500000 / HZ)); #elif HZ < ((1000 / MAX_UDELAY_MS) << 1) usecs *= (0x8000000000000000UL / (500000 / HZ)) >> 1; lpj <<= 1 #elif HZ < ((1000 / MAX_UDELAY_MS) << 2) usecs *= (0x8000000000000000UL / (500000 / HZ)) >> 2; lpj <<= 2 #else usecs *= (0x8000000000000000UL / (500000 / HZ)) >> 3; lpj <<= 3 #endif Any idea? --- Atsushi Nemoto
