linux-kernel - Re: [PATCH] clocksource: sh_tmu: Set cpu_possible

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Date:	Tue, 16 Dec 2014 20:46:33 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	SH-Linux <linux-sh@...r.kernel.org>,
	"Simon Horman [Horms]" <horms@...ge.net.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] clocksource: sh_tmu: Set cpu_possible_mask to fix SMP broadcast

Hi Laurent,

On Tue, Dec 16, 2014 at 8:20 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Daniel,
>
> On Tuesday 16 December 2014 12:14:40 Daniel Lezcano wrote:
>> On 12/16/2014 10:48 AM, Magnus Damm wrote:
>> > From: Magnus Damm <damm+renesas@...nsource.se>
>> >
>> > Update the TMU driver to use cpu_possible_mask as cpumask to make
>> > r8a7779 SMP work as expected with or without the ARM TWD timer.
>> >
>> > Signed-off-by: Magnus Damm <damm+renesas@...nsource.se>
>>
>> Applied as a 3.18 fix.
>
> You're a bit too fast, I haven't had time to review the patch yet.
>
>> ps: May I suggest to use the CLOCK_EVT_FEAT_DYNIRQ flag for this driver ?
>>
>> > ---
>> >
>> >   drivers/clocksource/sh_tmu.c |    2 +-
>> >   1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > --- 0001/drivers/clocksource/sh_tmu.c
>> > +++ work/drivers/clocksource/sh_tmu.c       2014-12-16 17:49:49.000000000 +0900
>> > @@ -428,7 +428,7 @@ static void sh_tmu_register_clockevent(s
>> >
>> >     ced->features = CLOCK_EVT_FEAT_PERIODIC;
>> >     ced->features |= CLOCK_EVT_FEAT_ONESHOT;
>> >     ced->rating = 200;
>> > -   ced->cpumask = cpumask_of(0);
>> > +   ced->cpumask = cpu_possible_mask;
>
> Magnus, how thoroughly have you tested this ? The TMU is indeed usable by all
> CPUs, so setting the CPU mask to cpu_possible_mask makes sense, but last time
> I've tried that it broke the broadcast timer due to the heuristics used by the
> clock events core code.

Uhm, so I've tested this particular patch on r8a7779 but I do agree
that the TMU is used on a bunch of SoCs if that's what you mean. I
don't see how it is different from any other of our timers though, and
those got fixed like this earlier.

I wonder if you may recall an earlier issue with incorrect clock event
priorities and code somehow working-by-accident without the mask set
as expected?

> Could you please confirm that you've tested both CONFIG_PREEMPT_NONE and
> CONFIG_PREEMPT with and without the ARM TWD times, and that you've booted to
> userspace and tested timer broadcast on all CPUs ?

No I have not. I've booted to user space in initramfs with DT-based
TWD on Multiplatform for r8a7779. Without this fix (and other r8a7779
TWD bits) I see a lot of breakage. For instance, TWD and SMP boot is
broken on r8a7779 - both legacy and non-legacy. I have not gotten to
sh73a0 yet, but I assume it is busted too.

Can you please explain to me how the TMU is any different compared to
the CMT, MTU2 or STI? =)

And no, I don't have any r8a7740 board anymore. Can anyone else test?

Cheers,

/ magnus
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