From: Arnd Bergmann <arnd@arndb.de>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: "linux-kernel@vger.kernel.org" <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,
Parisc List <linux-parisc@vger.kernel.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 13/13] m68k: mac: convert to generic clockevent
Date: Sat, 10 Oct 2020 20:52:01 +0200 [thread overview]
Message-ID: <CAK8P3a3rM7gJjdTtcKzr6yi15n6xs-yhEpmSOf3QHfahQwxqkw@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.23.453.2010091900150.12@nippy.intranet>
On Sat, Oct 10, 2020 at 12:21 AM Finn Thain <fthain@telegraphics.com.au> wrote:
>
> 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.
Yes, correct. I marked this patch as RFC instead of PATCH, as I'm
just trying to find out where it should be headed. I would hope the
other patches can just get merged.
> On m68k, HZ is fixed at 100. Without addressing that, would there be any
> benefit from adopting GENERIC_CLOCKEVENTS as per this RFC patch?
I don't think so, I mainly did it to see if there is a problem with mixing
the two modes, and I couldn't find any. The behavior seems unchanged
before and after my patch, the main difference being a few extra kilobytes
in kernel .text for the generic clockevents code.
> 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.
Good point, though I would be surprised if anything went wrong with
this patch on real hardware but not in emulation, as all the register-level
interactions with the timer are the same.
Adding oneshot mode is a completely different matter though, that
clearly needs to be tested on real hardware.
> > 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.
Ah, good. This is partly what I had been hoping for, as my patch
can be used as a starting point for that if you want to give it a go.
Arnd
next prev parent reply other threads:[~2020-10-10 22:51 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
2020-10-10 18:52 ` Arnd Bergmann [this message]
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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