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-rw-r--r--arch/powerpc/cpu/mpc8xxx/ddr/util.c56
1 files changed, 40 insertions, 16 deletions
diff --git a/arch/powerpc/cpu/mpc8xxx/ddr/util.c b/arch/powerpc/cpu/mpc8xxx/ddr/util.c
index b9a5a69..02908b4 100644
--- a/arch/powerpc/cpu/mpc8xxx/ddr/util.c
+++ b/arch/powerpc/cpu/mpc8xxx/ddr/util.c
@@ -8,9 +8,17 @@
#include <common.h>
#include <asm/fsl_law.h>
+#include <div64.h>
#include "ddr.h"
+/* To avoid 64-bit full-divides, we factor this here */
+#define ULL_2e12 2000000000000ULL
+#define UL_5pow12 244140625UL
+#define UL_2pow13 (1UL << 13)
+
+#define ULL_8Fs 0xFFFFFFFFULL
+
/*
* Round mclk_ps to nearest 10 ps in memory controller code.
*
@@ -20,35 +28,51 @@
*/
unsigned int get_memory_clk_period_ps(void)
{
- unsigned int mclk_ps;
+ unsigned int data_rate = get_ddr_freq(0);
+ unsigned int result;
+
+ /* Round to nearest 10ps, being careful about 64-bit multiply/divide */
+ unsigned long long mclk_ps = ULL_2e12;
- mclk_ps = 2000000000000ULL / get_ddr_freq(0);
- /* round to nearest 10 ps */
- return 10 * ((mclk_ps + 5) / 10);
+ /* Add 5*data_rate, for rounding */
+ mclk_ps += 5*(unsigned long long)data_rate;
+
+ /* Now perform the big divide, the result fits in 32-bits */
+ do_div(mclk_ps, data_rate);
+ result = mclk_ps;
+
+ /* We still need to round to 10ps */
+ return 10 * (result/10);
}
/* Convert picoseconds into DRAM clock cycles (rounding up if needed). */
unsigned int picos_to_mclk(unsigned int picos)
{
- const unsigned long long ULL_2e12 = 2000000000000ULL;
- const unsigned long long ULL_8Fs = 0xFFFFFFFFULL;
- unsigned long long clks;
- unsigned long long clks_temp;
+ unsigned long long clks, clks_rem;
+ /* Short circuit for zero picos */
if (!picos)
return 0;
- clks = get_ddr_freq(0) * (unsigned long long) picos;
- clks_temp = clks;
- clks = clks / ULL_2e12;
- if (clks_temp % ULL_2e12) {
+ /* First multiply the time by the data rate (32x32 => 64) */
+ clks = picos * (unsigned long long)get_ddr_freq(0);
+
+ /*
+ * 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 >>= 13;
+
+ /* If we had a remainder, then round up */
+ if (clks_rem)
clks++;
- }
- if (clks > ULL_8Fs) {
+ /* Clamp to the maximum representable value */
+ if (clks > ULL_8Fs)
clks = ULL_8Fs;
- }
-
return (unsigned int) clks;
}