[Letux-kernel] 1.5GHz problems

[H. Nikolaus Schaller]

> Am 29.07.2016 um 19:45 schrieb Grazvydas Ignotas <notasas at gmail.com>:
> 
> On Fri, Jul 29, 2016 at 5:00 PM, H. Nikolaus Schaller <hns at goldelico.com> wrote:
>> 
>> G) [Kernel] omap5 mpu bridge dividers
>> Matthijs recently reported a potential issue here with the above subject
>> line.
>> 
>> A simple test would be to boot at 1.5Ghz and then run
>> 
>> omapconf write 0x4A004320 0x06000001
>> 
>> But I can't even boot at 1.5Ghz so I have no chance to test.
> 
> It used to be possible to select default cpufreq governor in .config
> or maybe kernel arguments, so perhaps you could try booting with
> powersave governor, change the divider and then switch to the
> performance governor.

good idea!

Was a little more difficult. I had to

1. change defconfig
# CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
-# CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
+CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE=y
# CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
-CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
+# CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set

2. echo "ENABLE=false" >$SD/etc/default/cpufrequtils
or Debian would try to enable the ondemand govenor at the end of the
boot process.

3. After adding two OPP for 1.25GHz and 1.5GHz to DT I could run
additional tests.

cpufreq-set -f 1Ghz	runs fine. No problems.
cpufreq-set -f 1.25GHz might hang
cpufreq-set -f 1.5GHz hangs almost immediately within a second or so. Even as the CPU is almost idle (waiting for shell and blinking LEDs)

4. Clock divider
devmem2 0x4A004320 w 0x06000001
/dev/mem opened.
Memory mapped at address 0xb6fae000.
Value at address 0x4A004320 (0xb6fae320): 0x1000001
Written 0x6000001; readback 0x6000001

has no obvious influence. Neither @500 MHz nor @1.5GHz.

So unfortunately we do not know more than before.

The only thing that remains really stable is that the board is instable @>1GHz.

We simply do not know the handle to turn for an improvement.
And we all can imagine a lot of handles... The trick is to find the
right one.

BR,
Nikolaus