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    SubjectRe: [PATCH 46/58] clocksource/drivers: Add a new driver for the Atmel ARM TC blocks
    On 08/06/2017 at 09:44:46 +0200, Daniel Lezcano wrote:
    >
    > +Mark Rutland, +Rob Herring
    >
    >
    > Alexandre, Boris, have a look at https://www.spinics.net/lists/arm-kernel/msg572652.html
    >
    > That will tell you the story.
    >

    Ok, so is the solution putting the driver back in mach-at91 were we can
    do whatever we want like mach-omap2 is doing?

    > On Thu, Jun 08, 2017 at 07:42:36AM +0200, Boris Brezillon wrote:
    > > Le Thu, 8 Jun 2017 01:17:15 +0200,
    > > Alexandre Belloni <alexandre.belloni@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>;
    > > };
    > > };
    >
    > --
    >
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    --
    Alexandre Belloni, Free Electrons
    Embedded Linux and Kernel engineering
    http://free-electrons.com

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