[PATCH] arm: omap2: Kconfig: select TWD and global timer on AM43xx devices

On 11/13/2015 02:48 PM, Grygorii Strashko wrote:

On 11/12/2015 08:06 PM, Felipe Balbi wrote:

quoted

Make sure to tell the kernel that AM437x has
TWD and global timers.

Signed-off-by: Felipe Balbi <redacted>
---

Hi Tony,

now that all dependencies are in place, we can
finally enable twd and global_timer for AM437x.

I'd appreciated if someone can clarify if all described below is valid.
(may be some questions are dummy - sorry).

After all last changes related to TI OMAP clock source/clock event/sched clock's
devices configuration we will have the following for am437x case:

clockevents:
  "timer1",	clockevent_gpt, .rating = 300, CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, ti,timer-alwon,
  "arm,twd-timer",	twd_evt,.rating = 350, CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP
  "arm_global_timer",	 gt_evt, rating = 300, CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERCPU

clocksources:
  "jiffies", clocksource_jiffies,  rating = 1
  if use_gptimer_clksrc
	"timer2", clocksource_gpt, .rating = 300, CLOCK_SOURCE_IS_CONTINUOUS,
	|-sched_clock_register(dmtimer_read_sched_clock, 32, clksrc.rate);
  else
	"ti,omap-counter32k", ti_32k_timer, .rating = 250, CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_SUSPEND_NONSTOP,
	|-sched_clock_register(omap_32k_read_sched_clock, 32, 32768);

  "arm,global-timer", gt_clocksource, .rating = 300, CLOCK_SOURCE_IS_CONTINUOUS
  |-sched_clock_register(gt_sched_clock_read, 64, gt_clk_rate);

1) current clockevent device will be registered during registration of clockevent devices
and it will be  "arm,twd-timer" - processing sequence follows the way they are listed above.

2) current clocksource will be selected from fs_initcall(clocksource_done_booting);
and it will be "arm,global-timer" or "timer2" if use_gptimer_clksrc

3) sched clock: "arm,global-timer" will be selected as sched_clock *always*,
because it depend on Makefile order (if someone will decide to sort entries
in drivers/clocksource/Makefile then "ti,omap-counter32k" most probably will
be always selected as sched clock).

Ok. Sry. Above is not completely true. There are no dependency on makefile
and sched clock with Max freq will be selected - and never changed even if
corresponding clocksource can be changed through sysfs.

Uh..

As for me, "timer1" is selected as clockevent device incorrectly, because it's
  ti,timer-alwon.

I think, "ti,omap-counter32k" will crash if use_gptimer_clksrc == true, because
corresponding HWmod will not be enabled (not tested this case).

Ok. Below is confirmation for the case if use_gptimer_clksrc == true, so
https://www.spinics.net/lists/linux-omap/msg122576.html
"[PATCH 00/11] arm: omap: counter32k rework" introduces regression !?

cat /sys/devices/system/clocksource/clocksource0/available_clocksource 
timer2 arm_global_timer 32k_counter 
/ # echo 32k_counter > /sys/devices/system/clocksource/clocksource0/current_cloc
ksource 
[  102.194313] Unhandled fault: imprecise external abort (0x1406) at 0x0020ab5c
[  102.197862] pgd = ee22c000





-- 
regards,
-grygorii