linux-kernel - Re: [PATCH 7/9] clocksource/drivers/rockchip

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Message-ID: <28466016.LeLsKNAIhE@diego>
Date:   Thu, 24 Nov 2016 15:32:39 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Alexander Kochetkov <al.kochet@...il.com>
Cc:     daniel.lezcano@...aro.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH 7/9] clocksource/drivers/rockchip_timer: implement clocksource timer

Am Donnerstag, 24. November 2016, 17:14:56 schrieb Alexander Kochetkov:
> > 24 нояб. 2016 г., в 16:21, Heiko Stübner <heiko@...ech.de> написал(а):
> > 
> > what I actually meant was that the driver could also recognize the rk3188-
> > timer compatible as "we need a clocksource" and it shouldn't matter which
> > timer actually gets used for this.
> 
> One rockchip timer cannot be used as clockevent and clocksource at the same
> time.
> 
> In case of clockevent we want interrupts from it at specified times. So we
> load one value into timer counter and it generates an interrupt.
> 
> In case of clocksource we load max value into timer counter, run timer and
> read current value on demand.
> 
> rockchip_timer driver currently implement clockevent. So, if I create only
> one timer in the device tree, it should be clockevent timer. As that
> behavior already expected from driver by people used it.
> 
> I may suggest such solution here: if I want clocksource, I have to declare
> two timer in device tree. First probed timer would be clockevent and second
> one would be clocksource. All other timers will be ignored. Is that
> solution good?

yep, sounds good, especially as with your patch 9/9 you already declare these 
necessary timers.

> If I want one timer and want it be clocksource not clockevent how that
> situation should be configured? Device tree not good for this. Kconfig not
> good. Pass that configuration on kernel command line?

simply ignore that case :-)

I.e. newer kernels are supposed to be able to run old devicetrees and in that 
case they will have the global-timer as (slightly unstable) clocksource.

Also on the cortex-a9 we also still have the smp-twd as clockevent device.

Heiko