From: Andres Salomon <dilinger@queued.net>
To: Jens Rottmann <JRottmann@LiPPERTEmbedded.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, linux-geode@lists.infradead.org
Subject: Re: IRQF_TIMER | IRQF_SHARED ?
Date: Mon, 12 Dec 2011 12:31:31 -0800 [thread overview]
Message-ID: <20111212123131.502be350@queued.net> (raw)
In-Reply-To: <4EE620A5.7080402@LiPPERTEmbedded.de>
On Mon, 12 Dec 2011 16:41:25 +0100
Jens Rottmann <JRottmann@LiPPERTEmbedded.de> wrote:
> Hi Andres,
>
> one of our customers tripped over the fact that the MFGPT driver
> won't share its IRQ with anyone else. (MFGPT defaulted to same IRQ as
> audio, MFGPT driver loaded first, audio fails.) *No big deal!* They
> don't actually need MFGPT and will simply disable it. It just made me
> wonder ...
>
> Why would it be such a bad idea to use IRQF_TIMER | IRQF_SHARED (see
> patch below)? mfgpt_tick() already does properly return IRQ_NONE when
> it feels unresponsible. I tested it with either driver loaded first
> and it seemed to work (well, at least audio worked, don't know how to
> explicitly test cs5535-clockevt).
Just loading cs5535-clockevt should start the periodic timer. On my
XO-1, IRQ 7 starts firing immediately.
>
> I thought about latencies of IRQ sharing being unacceptable for a
> timer, but ...
> - If MFGPT is loaded first there is no additional latency, is there?
> Audio recieves its IRQs only as 2nd in list but that's not a problem.
> - If MFGPT is loaded second - well, there is a latency, but without
> sharing the IRQ the driver failed to load at all, so that's still an
> improvement.
>
> But I did not fail to notice that _none_ of the code in
> drivers/clocksource/ uses IRQF_SHARED, obviously this must be
> deliberate.
Hm, maybe tglx knows? For my part, I don't think it would be a
problem, but I can imagine the reason for not sharing being clock drift
or something to that effect.
>
> So, what's so bad about IRQF_TIMER | IRQF_SHARED?
>
> Any education would be welcome, even if combined with flame. :-)
>
> Thanks and best regards,
> Jens
>
> --- linux-3.2-rc4/drivers/clocksource/cs5535-clockevt.c
> +++ shared_mfgpt_irq/drivers/clocksource/cs5535-clockevt.c
> @@ -133,7 +133,7 @@ static irqreturn_t mfgpt_tick(int irq, v
>
> static struct irqaction mfgptirq = {
> .handler = mfgpt_tick,
> - .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER,
> + .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER |
> IRQF_SHARED, .name = DRV_NAME,
> };
>
> _
>
next prev parent reply other threads:[~2011-12-12 20:41 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-12 15:41 IRQF_TIMER | IRQF_SHARED ? Jens Rottmann
2011-12-12 20:31 ` Andres Salomon [this message]
2011-12-12 21:00 ` Martin-Éric Racine
2011-12-12 22:06 ` Andres Salomon
2011-12-12 23:38 ` Thomas Gleixner
2011-12-13 15:49 ` Jens Rottmann
2011-12-14 18:37 ` Jens Rottmann
2011-12-14 18:47 ` Andres Salomon
2011-12-21 15:42 ` [PATCH] cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels Jens Rottmann
2012-01-11 10:10 ` Andres Salomon
2012-01-19 12:57 ` Jens Rottmann
2012-01-23 10:44 ` Andres Salomon
2011-12-21 16:37 ` IRQF_TIMER | IRQF_SHARED ? Jens Rottmann
2011-12-22 16:35 ` [PATCH] cs5535-clockevt: allow the MFGPT IRQ to be shared Jens Rottmann
2012-01-11 10:15 ` Andres Salomon
2012-01-30 13:51 ` [PATCH] cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels Jens Rottmann
2012-01-30 13:59 ` [PATCH] cs5535-clockevt: allow the MFGPT IRQ to be shared Jens Rottmann
2012-02-06 8:20 ` [PATCH resend] cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels Jens Rottmann
2012-02-06 8:23 ` [PATCH resend] cs5535-clockevt: allow the MFGPT IRQ to be shared Jens Rottmann
2011-12-19 14:32 ` "clockevents: Set noop handler in clockevents_exchange_device()" causes hang with cs5535-clockevt Jens Rottmann
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