dt-bindings: Add doc for the Ingenic TCU drivers
Quoted 58 lines · Alexandre Belloni
Quoted 56 lines · Paul Cercueil
Quoted 25 lines · Daniel Lezcano
On 31/07/2018 00:01, Paul Cercueil wrote:
[ ... ]
Quoted 12 lines
Quoted 12 lines
Quoted 11 lines
+- ingenic,timer-channel: Specifies the TCU channel that should be used as
+ system timer. If not provided, the TCU channel 0 is used for the system timer.
+
+- ingenic,clocksource-channel: Specifies the TCU channel that should be used
+ as clocksource andsched_clock. It must be a different channel than the one
+ used as system timer. If not provided, neither a clocksource nor a +sched_clockis instantiated.Quoted 7 lines
Quoted 7 lines
clocksource and
sched_clockare Linux specific and don't belong in DT. You should define properties of the hardware or use existing properties like interrupts or clocks to figure out which channel to use. For example, if some channels don't have an interrupt, then use them for clocksource and not a clockevent. Or you could have timers that run in low-power modes or not. If all the channels are identical, then it shouldn't matter which ones the OS picks.Quoted 2 lines
It can't work in this case because the pmw and the timer driver are not communicating and the first one can stole a channel to the last one.
In that particular case the timer driver will always request its channels first; with no timer set the system hangs before
subsys_initcall, and the PWM driver is a subnode of the timer node, so is probed only after the timer probed.Quoted 11 lines
Quoted 10 lines
We already talked about that. All the TCU channels can be used for PWM. The problem is I cannot know from the driver's scope which channels will be free and which channels will be requested for PWM. You suggested that I parse the devicetree for clients, and I did that in the V3/V4 patchset. But it only works for clients requesting through devicetree, not from platform code or even sysfs.
One thing I can try is to dynamically change the channels the system timer and clocksource are using when the current ones are requested for PWM. But that sounds hardcore...
Quoted 8 lines
Yes, it is :/
Sorry for letting you wasting time and effort to write an overkill code not suitable for upstream.
A very gross thought, wouldn't be possible to "register" a channel from the timer driver code in a shared data area (but well self-encapsulated) and the pwm code will check such channel isn't in use ?
Probably, but it's the contrary I need to do. The timer driver code can use any channel, and probes first. The PWM driver code must use specific channels, and probes last. So either the timer driver knows what channels it can't use, thanks to a device property, or it adapts itself when a channel in use is requested for PWM, which is what I tried in v7.
I think we could find a way to use a devicetree property that doesn't trigger Rob. That would still be the easiest and cleanest solution.
Quoted 8 lines
Quoted 2 lines
Maybe "ingenic,reserved-channels-mask", which would contain a mask of channels that can only be used by the timer driver. And what the timer driver does with these channels, would be specific to the implementation and would not appear in the bindings. I hope Rob can work with that.
Rob did ack the following binding:
another subdevice is a PWM (not documented here).
I'm not sure that it would be the cleanest in my case, my PWM and watchdog sub-nodes already specify memory resources in their "reg" property. And if I add memory resources to the same "timers" sub-nodes as in your example, the ranges will overlap and Rob still won't be happy :)
-Paul