RE: [PATCH 1/2] clocksource/drivers/ostm: Delay driver registration

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On Tuesday, September 11, 2018 1, Rob Herring wrote:
> Well before we get to initcalls, the kernel calls the arch specific
> time_init() which (on ARM) calls of_clk_init (for all the reasons
> above) and then timer_probe(). When timer_probe returns, it is
> expected that you have setup a clocksource and clockevent. If you
> haven't, then at some point before we get to initcalls we should hang
> because we're not getting any timer interrupts and time is not
> advancing.

What I get now is:

[    0.000000] timer_probe: no matching timers found
...
...
 [    0.000000] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
...
...


But then later on in boot, I'll get (with my subsys_initcall timer fix)

...
...
[    0.000000] SCSI subsystem initialized
[    0.000000] usbcore: registered new interface driver usbfs
[    0.000000] usbcore: registered new interface driver hub
[    0.000000] usbcore: registered new device driver usb
[    0.000000] clocksource: ostm: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 28958491609 ns
[    0.000619] sched_clock: 32 bits at 66MHz, resolution 15ns, wraps every 32537631224ns
[    0.008599] ostm: used for clocksource
[    0.018926] ostm: used for clock events
[    0.133339] clocksource: Switched to clocksource ostm
[    0.821474] NET: Registered protocol family 2
[    0.840624] tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 4096 bytes)
[    0.850549] TCP established hash table entries: 1024 (order: 0, 4096 bytes)
...
...



> Maybe you
> just get lucky and it works as long as no thread blocks (e.g. on a
> msleep).

You're right. If I put in a msleep() before my timer is up and running, it hangs.

As far as I can tell, nothing before device_initcall seems to call anything like msleep.

> If things changed and you can setup a timer in an initcall,
> then why are folks still trying to do things like early platform
> drivers. Regular drivers would work and we should be able to
> completely remove CLK_OF_DECLARE and TIMER_OF_DECLARE.

I wonder if the reason is because you can't assign a priority to your 
driver when you declare it with xxx_initcall( ). So, your driver ends up 
in the same table as all the other drivers and you are not guaranteed the
order in which they probe. So, the answer was to make a NEW table and 
register it using TIMER_OF_DECLARE and CLOCK_OF_DECLARE.

I wonder they just didn't make a clock_initcall() and timer_initcall() 
instead.

Chris




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