lkml.org 
[lkml]   [2017]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 46/58] clocksource/drivers: Add a new driver for the Atmel ARM TC blocks

+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.

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>;
> };
> };

--

<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

\
 
 \ /
  Last update: 2017-06-12 01:23    [W:0.121 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site