linux-kernel - Re: [PATCH v5 1/8] clocksource: dmtimer: Remove all the exports

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Date:   Wed, 13 Dec 2017 10:15:27 +0100
From:   Ladislav Michl <ladis@...ux-mips.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Keerthy <j-keerthy@...com>, daniel.lezcano@...aro.org,
        aaro.koskinen@....fi, thierry.reding@...il.com,
        grygorii.strashko@...com, linux-omap@...r.kernel.org,
        robh+dt@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pwm@...r.kernel.org, sebastian.reichel@...labora.co.uk,
        linux-kernel@...r.kernel.org, t-kristo@...com,
        linux@...linux.org.uk
Subject: Re: [PATCH v5 1/8] clocksource: dmtimer: Remove all the exports

On Tue, Dec 12, 2017 at 10:21:50AM -0800, Tony Lindgren wrote:
> * Ladislav Michl <ladis@...ux-mips.org> [171212 18:06]:
> > I do not follow. Each general-purpose timer module has its own interrupt line,
> > so claiming that irq directly using request_irq seems enough. Could you
> > explain interrupt controller idea a bit more?
> 
> Well let's assume we have drivers/clocksource/timer-dm.c implement
> an irq controller. Then the pwm driver would just do:
> 
> pwm9: dmtimer-pwm {
> 	compatible = "ti,omap-dmtimer-pwm";
> 	#pwm-cells = <3>;
> 	ti,timers = <&timer9>;
> 	ti,clock-source = <0x00>; /* timer_sys_ck */
> 	interrupts-extended = <&timer9 IRQ_TYPE_SOMETHING>;
> };
> 
> Then you can do whatever you need to in the pwm driver with
> enable_irq/disable_irq + a handler?

That seems to work. Now should we map 1:1 to timer interrupt or
have separate interrupt for match, overflow and capture?
Former would need some more dm_timer_ops to determine interrupt
source, while later would work "automagically" - but I haven't
tested it yet.

> If reading the line status is needed.. Then maybe the GPIO framework
> needs to have hardware timer support instead?

It does not seem OMAP can read event pin value in event capture mode.

> Anyways, just thinking out loud how we could have a Linux generic
> hardware timer framework that drivers like pwm could then use.

I need a bit longer chain:
dmtimer -> pwm -> rc (which calls ir_raw_event_store from interrupt)
Is extending pwm core with interrpt callback the right thing there?
Something like:
(*pulse_captured)(ktime_t width, ktime_t last_edge);

Thank you,
	ladis