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author | Anton Vorontsov <avorontsov@ru.mvista.com> | 2008-02-22 06:45:08 +1100 |
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committer | Paul Mackerras <paulus@samba.org> | 2008-02-26 22:17:03 +1100 |
commit | 50530378161fa8d7837243119ed9140ee65e55d4 (patch) | |
tree | b3ae4e02f34a9d115bb4cf703ac19b17ec13688b /include/asm-powerpc | |
parent | d9d1063d47cbfe45f8b369475a35c3cdd64fb69c (diff) | |
download | op-kernel-dev-50530378161fa8d7837243119ed9140ee65e55d4.zip op-kernel-dev-50530378161fa8d7837243119ed9140ee65e55d4.tar.gz |
[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 'include/asm-powerpc')
0 files changed, 0 insertions, 0 deletions