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[POWERPC] 8xx: Timebase frequency should not depend on bus-frequency

Browse source 
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>
This commit is contained in:
Anton Vorontsov 2008-02-22 06:45:08 +11:00 committed by Paul Mackerras
parent d9d1063d47
commit 5053037816
1 changed files with 1 additions and 6 deletions
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7
arch/powerpc/platforms/8xx/m8xx_setup.c
View file

@ -111,17 +111,12 @@ void __init mpc8xx_calibrate_decr(void)
/* Processor frequency is MHz.
*/
ppc_tb_freq = 50000000;
if (!get_freq("bus-frequency", &ppc_tb_freq)) {
printk(KERN_ERR "WARNING: Estimating decrementer frequency "
"(not found)\n");
}
ppc_tb_freq /= 16;
ppc_proc_freq = 50000000;
if (!get_freq("clock-frequency", &ppc_proc_freq))
printk(KERN_ERR "WARNING: Estimating processor frequency "
"(not found)\n");
ppc_tb_freq = ppc_proc_freq / 16;
printk("Decrementer Frequency = 0x%lx\n", ppc_tb_freq);
/* Perform some more timer/timebase initialization. This used