Reduce the calculation error to 1ps.
Signed-off-by: York Sun <york...@freescale.com>
---
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 104d360..c644131 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 */
--
1.7.0.4
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