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

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Date:   Tue, 12 Dec 2017 10:21:50 -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> [171212 18:06]:
> On Tue, Dec 12, 2017 at 09:00:54AM -0800, Tony Lindgren wrote:
> > Hmm what do you mean? We don't want to export tons of custom functions from
> > the timers in and then be in trouble when at some point we have a Linux
> > generic hw timer framework. We already had to deal with these custom
> > exports earlier with conversion to multiarch and then again with
> > device tree.
> >
> > For now, it's best to pass the timer information to the pwm driver in
> > platform data. In the long run that will be much easier to deal with than
> > fixing random drivers tinkering with the timer registers directly.
> 
> All that register access would happen only in drivers/clocksource/timer-dm.c?
> So platform data will hold all function pointers needed for event capture
> and the pwm driver will do only interface to pwm framework.

Yes please.

> > Ideally the pwm driver would just do a request_irq from the dmtimer code
> > where dmtimer code would implement an interrupt controller. That would
> > be already most fo the Linux generic hardware timer framework right there :)
> 
> 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?

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

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

Regards,

Tony