On 11-03-16 09:11, Sören Brinkmann wrote:
On Fri, 2016-03-11 at 09:00:14 +0100, Mike Looijmans wrote:
On 11-03-16 07:44, Mike Looijmans wrote:
...
The 'prescaler hack' is apparently still present in the 4.4 kernel code. The
problem is that it no longer works, not even on the speedgrade 1 devices (with
only 333 and 666 MHz setpoints).
Did a quick test on the board. The prescaler is applied correctly, so what's
causing the trouble?
# devmem 0xF8001000
0x00000015
# echo 333333 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
# devmem 0xF8001000
0x00000013
# echo 666666 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
# devmem 0xF8001000
0x00000015
Bits 1..4 are the prescaler values, at 666 it's set to 0b111 (7) and at 333
it's set to 0b110 (6). The register is a power-of-two value, so "7" means
2^8 and "6" means 2^7.
Are you sure the kernel is using the TTC and not GT? Especially on ARM
multi-arch kernels, the GT driver tends to be included in the kernel
and it will be used if available as the GT is the "better" clocksource,
compared to TTC.
Hmm, just manually hacking the register values has no effect at all on the
system. So apparently some other clock is being used as the source.
How can I see (and choose?) which clock is to be used?
Kind regards,
Mike Looijmans
System Expert
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