diff options
| author | Anton Vorontsov <avorontsov@ru.mvista.com> | 2008-02-21 22:45:08 +0300 |
|---|---|---|
| committer | Paul Mackerras <paulus@samba.org> | 2008-02-26 14:17:03 +0300 |
| commit | 50530378161fa8d7837243119ed9140ee65e55d4 (patch) | |
| tree | b3ae4e02f34a9d115bb4cf703ac19b17ec13688b /arch/powerpc/platforms/8xx | |
| parent | d9d1063d47cbfe45f8b369475a35c3cdd64fb69c (diff) | |
| download | linux-50530378161fa8d7837243119ed9140ee65e55d4.tar.xz | |
[POWERPC] 8xx: Timebase frequency should not depend on bus-frequency
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>
Diffstat (limited to 'arch/powerpc/platforms/8xx')
| -rw-r--r-- | arch/powerpc/platforms/8xx/m8xx_setup.c | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/arch/powerpc/platforms/8xx/m8xx_setup.c b/arch/powerpc/platforms/8xx/m8xx_setup.c index 184f998d1be2..0d9f75c74f8c 100644 --- a/arch/powerpc/platforms/8xx/m8xx_setup.c +++ b/arch/powerpc/platforms/8xx/m8xx_setup.c @@ -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 |