linux-kernel - Re: Writing clocksource driver, tips?

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Message-ID: <alpine.DEB.2.10.1409011029020.3333@nanos>
Date:	Mon, 1 Sep 2014 10:35:16 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Oleksij Rempel <linux@...pel-privat.de>
cc:	linux-kernel@...r.kernel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: Writing clocksource driver, tips?

On Sun, 31 Aug 2014, Oleksij Rempel wrote:
> - 1 timer can be used for clocksource other as  clock_event_device, how
> can i use other 2 timers on same controller. and how can i use other 3
> controllers?

All you need is two.

One for the clocksource (free running counter):

    100MHz is fine, it gives the timekeeping code nice
    granularity. There is no need for a wrap around interrupt. The
    core code knows how to deal with it.

The second one is for the clock event device

    Avoid a match timer if possible, it's a pain in the neck. Either a
    autoreloading timer for the periodic mode or a simple downcounting
    one for one shot mode is good enough.

The other timers are not of any value for Linux. Just leave them
alone.

Thanks,

	tglx
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