From 50530378161fa8d7837243119ed9140ee65e55d4 Mon Sep 17 00:00:00 2001 From: Anton Vorontsov Date: Fri, 22 Feb 2008 06:45:08 +1100 Subject: [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 Signed-off-by: Paul Mackerras --- arch/powerpc/platforms/8xx/m8xx_setup.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) (limited to 'arch/powerpc/platforms/8xx') diff --git a/arch/powerpc/platforms/8xx/m8xx_setup.c b/arch/powerpc/platforms/8xx/m8xx_setup.c index 184f998..0d9f75c 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 -- cgit v1.1