diff options
Diffstat (limited to 'arch/powerpc/cpu/mpc8xxx/ddr/util.c')
| -rw-r--r-- | arch/powerpc/cpu/mpc8xxx/ddr/util.c | 26 |
1 files changed, 11 insertions, 15 deletions
diff --git a/arch/powerpc/cpu/mpc8xxx/ddr/util.c b/arch/powerpc/cpu/mpc8xxx/ddr/util.c index 104d360a5f..c6441311c3 100644 --- a/arch/powerpc/cpu/mpc8xxx/ddr/util.c +++ b/arch/powerpc/cpu/mpc8xxx/ddr/util.c @@ -20,7 +20,8 @@ #define ULL_8FS 0xFFFFFFFFULL /* - * Round mclk_ps to nearest 10 ps in memory controller code. + * Round up mclk_ps to nearest 1 ps in memory controller code + * if the error is 0.5ps or more. * * If an imprecise data rate is too high due to rounding error * propagation, compute a suitably rounded mclk_ps to compute @@ -32,42 +33,37 @@ unsigned int get_memory_clk_period_ps(void) unsigned int result; /* Round to nearest 10ps, being careful about 64-bit multiply/divide */ - unsigned long long mclk_ps = ULL_2E12; - - /* Add 5*data_rate, for rounding */ - mclk_ps += 5*(unsigned long long)data_rate; + unsigned long long rem, mclk_ps = ULL_2E12; /* Now perform the big divide, the result fits in 32-bits */ - do_div(mclk_ps, data_rate); - result = mclk_ps; + rem = do_div(mclk_ps, data_rate); + result = (rem >= (data_rate >> 1)) ? mclk_ps + 1 : mclk_ps; - /* We still need to round to 10ps */ - return 10 * (result/10); + return result; } /* Convert picoseconds into DRAM clock cycles (rounding up if needed). */ unsigned int picos_to_mclk(unsigned int picos) { unsigned long long clks, clks_rem; + unsigned long data_rate = get_ddr_freq(0); /* Short circuit for zero picos */ if (!picos) return 0; /* First multiply the time by the data rate (32x32 => 64) */ - clks = picos * (unsigned long long)get_ddr_freq(0); - + clks = picos * (unsigned long long)data_rate; /* * Now divide by 5^12 and track the 32-bit remainder, then divide * by 2*(2^12) using shifts (and updating the remainder). */ clks_rem = do_div(clks, UL_5POW12); - clks_rem <<= 13; - clks_rem |= clks & (UL_2POW13-1); + clks_rem += (clks & (UL_2POW13-1)) * UL_5POW12; clks >>= 13; - /* If we had a remainder, then round up */ - if (clks_rem) + /* If we had a remainder greater than the 1ps error, then round up */ + if (clks_rem > data_rate) clks++; /* Clamp to the maximum representable value */ |
