[Letux-kernel] jz4730-i2c - clocksource

[H. Nikolaus Schaller]

> Am 06.03.2021 um 18:07 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> Maybe it is not THE issue but contributed. Basically a 16 bit counter
> should overflow only every 18 ms. This is more than a tick for HZ100.
> 
> It may only become a problem because something else stalls for more
> than 18 ms and blocks interrupt processing.
> 
> But 26 bit is on the safe side - and we have it. So there is no reason
> to work with the smallest reasonable width.
> 
> Ideal would be if 32 bits work, or 31.

Interestingly the CI20 tells with v5.11 kernel:

[    0.000000] clocksource: ingenic-timer: mask: 0xffff max_cycles: 0xffff, max_idle_ns: 38884100 ns
[    0.000001] sched_clock: 16 bits at 750kHz, resolution 1333ns, wraps every 43690000ns
[    0.100714] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
[    0.440673] clocksource: Switched to clocksource ingenic-timer


So it *is* running with 16 bits...
But the processor is faster serving any interrupts.

And it fails with our new letux-5.12-rc2 kernel.

So why is he CI20 loading the ingenic-timer at all? DTS says it should use the ingenic-ost...

Ok:

	tcu: timer at 10002000 {
		compatible = "ingenic,jz4780-tcu",
			     "ingenic,jz4770-tcu",
			     "simple-mfd";


TIMER_OF_DECLARE(jz4770_tcu_intc,  "ingenic,jz4770-tcu",  ingenic_tcu_init);

This means we are running our jz4730 extensions on the jz4770 as well.

BR,
Nikolaus