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

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Date:   Wed, 13 Dec 2017 08:51:10 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Ladislav Michl <ladis@...ux-mips.org>
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

* Ladislav Michl <ladis@...ux-mips.org> [171213 09:17]:
> 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.

Hmm the second option sounds appealing to me as then the device
tree binding really follows the hardware:

bit 2 capture interrupt
bit 1 overflow interrupt
bit 0 match interrupt

and in the dts we can describe these with:

interrupts-extended = <&timer 9 2 IRQ_TYPE_EDGE_SOMETHING>;
interrupts-extended = <&timer 9 1 IRQ_TYPE_EDGE_SOMETHING>;
interrupts-extended = <&timer 9 0 IRQ_TYPE_EDGE_SOMETHING>;

I think these are all edge based on "Capture Mode Functionality"
chapter in the TRM?

> > 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.

Sounds like a bug somehwere, probably in software?

> > 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);

OK seems like having drivers/clocksource/timer-dm.c a chained
interrupt handler should do it :) Anyways, that's a different
set of patches on top of these.

Regards,

Tony