From: Finn Thain <fthain@telegraphics.com.au>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-kernel@vger.kernel.org,
Russell King <linux@armlinux.org.uk>,
Tony Luck <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Greg Ungerer <gerg@linux-m68k.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Philip Blundell <philb@gnu.org>,
Joshua Thompson <funaho@jurai.org>, Sam Creasey <sammy@sammy.net>,
"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
Helge Deller <deller@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
John Stultz <john.stultz@linaro.org>,
Stephen Boyd <sboyd@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
linux-m68k@lists.linux-m68k.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC 13/13] m68k: mac: convert to generic clockevent
Date: Sat, 10 Oct 2020 09:21:38 +1100 (AEDT) [thread overview]
Message-ID: <alpine.LNX.2.23.453.2010091900150.12@nippy.intranet> (raw)
In-Reply-To: <20201008154651.1901126-14-arnd@arndb.de>
Hi Arnd,
Perhaps patch 13 does not belong in this series (?).
All m68k platforms will need conversion before the TODO can be removed
from Documentation/features/time/clockevents/arch-support.txt.
On m68k, HZ is fixed at 100. Without addressing that, would there be any
benefit from adopting GENERIC_CLOCKEVENTS as per this RFC patch?
On Thu, 8 Oct 2020, Arnd Bergmann wrote:
> Now that the infrastructure allows kernels to have both legacy timer
> ticks and clockevent drivers in the same image, start by moving one
> platform to generic clockevents.
>
> As qemu only supports the q800 platform among the classic m68k, use that
> as an example.
>
Correct VIA emulation is suprisingly difficult, so this kind of work
should be tested on real hardware.
I say that because when I did the clocksource conversion for m68k I ran
into a bug in QEMU (since fixed) and also because I once worked on some of
the bugs in the emulated VIA device used in MAME/MESS.
> I also tried adding oneshot mode, which was successful but broke the
> clocksource. It's probably not hard to make it work properly, but this
> is where I've stopped.
>
I'm not so sure that one timer is able to support both a clocksource
driver and a clockevent driver. In some cases we may have to drop the
clocksource driver (i.e. fall back on the jiffies clocksource).
Anyway, even on Macs with only one VIA chip we still have two timers. So I
think we should try to use Timer 1 as a freerunning clocksource and Timer
2 as a oneshot clock event. This may result in better accuracy and simpler
code. This may require some experimentation though.
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> I have never tried implementing a clockevent or clocksource
> driver in the past, so this is really just an experiment and
> I expect I got something wrong.
>
Writing clockevent drivers is new to me too. I'm still trying to discover
what the implications might be if the only available clockevent device
offers oneshot mode or periodic mode but not both.
next prev parent reply other threads:[~2020-10-09 22:21 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 15:46 [PATCH 00/13] Clean up legacy clock tick users Arnd Bergmann
2020-10-08 15:46 ` [PATCH 01/13] timekeeping: add CONFIG_LEGACY_TIMER_TICK Arnd Bergmann
2020-10-09 22:18 ` Finn Thain
2020-10-10 20:31 ` Arnd Bergmann
2020-10-12 13:14 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 02/13] ia64: convert to legacy_timer_tick Arnd Bergmann
2020-10-08 15:46 ` [PATCH 03/13] ARM: rpc: use legacy_timer_tick Arnd Bergmann
2020-10-08 15:46 ` [PATCH 04/13] parisc: " Arnd Bergmann
2020-10-08 15:46 ` [PATCH 05/13] m68k: coldfire: use legacy_timer_tick() Arnd Bergmann
2020-10-09 12:53 ` Greg Ungerer
2020-10-09 13:23 ` Arnd Bergmann
2020-10-08 15:46 ` [PATCH 06/13] m68k: split heartbeat out of timer function Arnd Bergmann
2020-10-12 13:14 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 07/13] m68k: sun3/sun3c: use legacy_timer_tick Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 08/13] m68k: m68328: use legacy_timer_tick() Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-12 15:30 ` Arnd Bergmann
2020-10-12 20:33 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 09/13] m68k: change remaining timers to legacy_timer_tick Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 10/13] m68k: remove timer_interrupt() function Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-08 15:46 ` [PATCH 11/13] timekeeping: remove xtime_update Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-12 13:37 ` Arnd Bergmann
2020-10-12 20:44 ` Thomas Gleixner
2020-10-08 15:46 ` [PATCH 12/13] timekeeping: default GENERIC_CLOCKEVENTS to enabled Arnd Bergmann
2020-10-12 13:15 ` Geert Uytterhoeven
2020-10-08 15:46 ` [RFC 13/13] m68k: mac: convert to generic clockevent Arnd Bergmann
2020-10-09 22:21 ` Finn Thain [this message]
2020-10-10 18:52 ` Arnd Bergmann
2020-10-15 1:18 ` Finn Thain
[not found] ` <CAK8P3a2ymv79j1edtJ983-VgjtxvT_6co7V0VRnHzcneW+0ZtA@mail.gmail.com>
2020-10-18 0:54 ` Finn Thain
[not found] ` <CAK8P3a3i6cum_9xGgsbxjXXvbRsP8Po5qLZ0Agb3c4gZTKC9GQ@mail.gmail.com>
2020-10-23 9:24 ` Geert Uytterhoeven
2020-10-25 12:45 ` Geert Uytterhoeven
2020-11-06 2:52 ` Finn Thain
2020-11-16 23:27 ` Sam Creasey
2020-10-30 0:41 ` Finn Thain
2020-10-30 13:12 ` Greg Ungerer
2020-11-06 3:12 ` Finn Thain
2020-10-12 22:18 ` [PATCH 00/13] Clean up legacy clock tick users Linus Walleij
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