[Letux-kernel] jz4730-i2c - clocksource

[H. Nikolaus Schaller]

Hi Paul,
I have switched to attempt a different debugging approach.

The key observation is that we can boot with clocksource=jiffies.
And we can switch through /sys to clocksource=ingenic-timer.

The ingenic-timer seems to be running well (incl. interrupts),
at least if I boot to login:

Here is some log what happens if we switch the clock source:


root at letux:~# cat /proc/interrupts 
           CPU0       
  2:     144402      MIPS   2  SoC intc cascade interrupt
  9:       1322      INTC   9  ttyS0
 14:       7368      INTC  14  10021000.mmc
 15:          0     GPIOA   0  matrix-keypad
 16:          0     GPIOA   1  matrix-keypad
 17:          0     GPIOA   2  matrix-keypad
 18:          0     GPIOA   3  matrix-keypad
 19:          0     GPIOA   4  matrix-keypad
 21:          0      INTC  21  13020000.dma
 24:     135738      INTC  24  TCU0
 29:          0     GPIOA   5  matrix-keypad
 31:          0     GPIOA   6  matrix-keypad
 32:          0     GPIOA   7  matrix-keypad
 33:          0     GPIOC   0  10021000.mmc cd
 34:          0     GPIOA  16  Touchpad Left
 35:          0     GPIOA  13  Touchpad Right
ERR:          0
root at letux:~# sleep 1;cat /proc/interrupts
           CPU0       
  2:     145675      MIPS   2  SoC intc cascade interrupt
  9:       1502      INTC   9  ttyS0
 14:       7368      INTC  14  10021000.mmc
 15:          0     GPIOA   0  matrix-keypad
 16:          0     GPIOA   1  matrix-keypad
 17:          0     GPIOA   2  matrix-keypad
 18:          0     GPIOA   3  matrix-keypad
 19:          0     GPIOA   4  matrix-keypad
 21:          0      INTC  21  13020000.dma
 24:     136831      INTC  24  TCU0
 29:          0     GPIOA   5  matrix-keypad
 31:          0     GPIOA   6  matrix-keypad
 32:          0     GPIOA   7  matrix-keypad
 33:          0     GPIOC   0  10021000.mmc cd
 34:          0     GPIOA  16  Touchpad Left
 35:          0     GPIOA  13  Touchpad Right
ERR:          0
root at letux:~# root at letux:~# cat clocksource 
echo available
cat /sys/devices/system/clocksource/clocksource0/available_clocksource
echo current
cat /sys/devices/system/clocksource/clocksource0/current_clocksource
sleep 1
echo switching
echo ingenic-timer >/sys/devices/system/clocksource/clocksource0/current_clocksource
for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
do
        date
        sleep 0.1
done
echo done
sleep 1
root at letux:~# ./clocksource 
available
ingenic-timer jiffies 
current
jiffies
switching
[  682.715103] clocksource: Switched to clocksource ingenic-timer
Thu Jan  1 00:11:15 UTC 1970

I interpret this as:
* TCU0 interrupts are working
* the only other interrupt being active seems to be ttyS0
* cevt based on TCU0 is in operation despite clocksource=jiffies
* there are background processes making use of it
* sleep 1 works with clocksource=jiffies
* the first "date" command after switching still succeeds
* sleep 0.1 hangs with clocksource=ingenic-timer

So the questions become:
* which subsystem is using or preferring "clocksource"?
* and why does it break down if we switch clocksource
* why is cevt using TCU0 in clocksource=jiffies mode? Priority?
* how does jiffies work if there is no other timer & interrupt?

BR,
Nikolaus