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authorAnton Vorontsov <avorontsov@ru.mvista.com>2008-02-22 06:45:08 +1100
committerPaul Mackerras <paulus@samba.org>2008-02-26 22:17:03 +1100
commit50530378161fa8d7837243119ed9140ee65e55d4 (patch)
treeb3ae4e02f34a9d115bb4cf703ac19b17ec13688b /arch/powerpc/platforms/8xx
parentd9d1063d47cbfe45f8b369475a35c3cdd64fb69c (diff)
[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.c7
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 184f998d1be..0d9f75c74f8 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