Le Thu, 8 Jun 2017 01:17:15 +0200,
Alexandre Belloni <alexandre.bell...@free-electrons.com> a écrit :
> On 07/06/2017 at 23:08:48 +0200, Daniel Lezcano wrote:
> > > I was going to agree but this is not flexible enough because the
> > > quadrature decoder always uses the first two channels. So on some
> > > products, we may have:
> > > - TCB0:
> > > o channels 0,1: qdec
> > > o channel 2: clocksource
> > >
> > > - TCB1:
> > > o channels 0,1: qdec
> > > o channel 2: clockevent
> > >
> > > This avoids wasting TCB channels.
> >
> > Ok. In this case you can check if the interrupt is specified for the node,
> > if
> > yes, then it is a clockevent.
> >
>
> But currently it is always specified in the SoC's dtsi. I don't find
> that too practical to push that to the board's dts. Also, lying by
> omission (the IRQ is always wired) in the DT is not different from
> having a property selecting which timer is the clocksource and which is
> the clockevent.
>
I agree with Alexandre here. Really, there's not much we can do to
detect which timer should be used as a clockevent and which one should
be used as a clocksource except explicitly specifying it in the DT.
Having an interrupt defined in one case (clockevent) and undefined in
the other case (clocksource), is just as hack-ish as the detection logic
Alexandre developed to avoid explicitly specifying the function
assigned to a specific timer.
Can we please find a solution that makes everyone happy (DT,
clocksoure/clockevent and at91 maintainers)?
How about adding a linux,timer-function property to specify which
function this timer is providing?
Something like that for example:
tcb0: timer@fff7c000 {
compatible = "atmel,at91rm9200-tcb", "simple-mfd", "syscon";
#address-cells = <1>;
#size-cells = <0>;
reg = <0xfff7c000 0x100>;
interrupts = <18 4>;
clocks = <&tcb0_clk>, <&clk32k>;
clock-names = "t0_clk", "slow_clk";
timer@0 {
compatible = "atmel,tcb-timer";
reg = <0>, <1>;
linux,timer-function = "clocksource";
};
timer@2 {
compatible = "atmel,tcb-timer";
reg = <2>;
linux,timer-function = "clockevent";
};
};
Alternatively, we could have a property or a node in chosen describing which
timer should be used:
chosen {
clockevent {
timer = <&timer2>;
};
clocksource {
timer = <&timer0>;
};
/*
* or
*
* clockevent = <&timer2>;
* clocksource = <&timer0>;
*
* but I think the clocksource/clockevent node approach
* is more future proof in case we need to add extra
* information like the expected resolution/precision or
* anything that could be tweakable.
*/
};
tcb0: timer@fff7c000 {
compatible = "atmel,at91rm9200-tcb", "simple-mfd", "syscon";
#address-cells = <1>;
#size-cells = <0>;
reg = <0xfff7c000 0x100>;
interrupts = <18 4>;
clocks = <&tcb0_clk>, <&clk32k>;
clock-names = "t0_clk", "slow_clk";
timer0: timer@0 {
compatible = "atmel,tcb-timer";
reg = <0>, <1>;
};
timer2: timer@2 {
compatible = "atmel,tcb-timer";
reg = <2>;
};
};
