Rewrote picos_to_clk() to avoid rounding errors.

Clarified that conversion is to DRAM clocks rather than platform clocks.
Made function static to spd_sdram.c.

Signed-off-by: James Yang <James.Yang@freescale.com>
Signed-off-by: Jon Loeliger <jdl@freescale.com>

diff --git a/cpu/mpc86xx/spd_sdram.c b/cpu/mpc86xx/spd_sdram.c
index ac9ff81ce602e1f9573254cfbcf5e26ef7ec3367..f37ab430b325bc2a2fc2c7df2a6859d36964baaf 100644 (file)
--- a/cpu/mpc86xx/spd_sdram.c
+++ b/cpu/mpc86xx/spd_sdram.c
@@ -51,20 +51,32 @@ extern int dma_xfer(void *dest, uint count, void *src);
 #define CFG_SUPER_BANK_INTERLEAVING    0
 
 /*
- * Convert picoseconds into clock cycles (rounding up if needed).
+ * Convert picoseconds into DRAM clock cycles (rounding up if needed).
  */
 
-int
-picos_to_clk(int picos)
+static unsigned int
+picos_to_clk(unsigned int picos)
 {
-       int clks;
-
-       clks = picos / (2000000000 / (get_bus_freq(0) / 1000));
-       if (picos % (2000000000 / (get_bus_freq(0) / 1000)) != 0) {
+       /* use unsigned long long to avoid rounding errors */
+       const unsigned long long ULL_2e12 = 2000000000000ULL;
+       unsigned long long clks;
+       unsigned long long clks_temp;
+
+       if (! picos)
+           return 0;
+
+       clks = get_bus_freq(0) * (unsigned long long) picos;
+       clks_temp = clks;
+       clks = clks / ULL_2e12;
+       if (clks_temp % ULL_2e12) {
                clks++;
        }
 
-       return clks;
+       if (clks > 0xFFFFFFFFULL) {
+               clks = 0xFFFFFFFFULL;
+       }
+
+       return (unsigned int) clks;
 }