m8xx_setup.c says:
/* Force all 8xx processors to use divide by 16 processor clock. */
And at the same time it is using bus-frequency for calculating
timebase. It is okay for most setups because bus-frequency is
equal to clock-frequency.
The problem emerges when cpu frequency is > 66MHz, quoting
u-boot/cpu/mpc8xx/speed.c:
if (gd->cpu_clk <= 66000000) {
sccr_reg |= SCCR_EBDF00; /* bus division factor = 1 */
gd->bus_clk = gd->cpu_clk;
} else {
sccr_reg |= SCCR_EBDF01; /* bus division factor = 2 */
gd->bus_clk = gd->cpu_clk / 2;
}
So in case of cpu clock > 66MHz, bus_clk = cpu_clk / 2. An then, from
Linux, we calculate timebase frequency as tb_freq = bus_clk / 16,
that is cpu_clk / 2 / 16, which is wrong.
This fixes the system time drifting problem on the EP885C board
running at 133MHz.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
5053037816