linux-kernel - Re: [PATCH 2/2] Convert PowerPC macro spin_event_timeout() to architecture independent macro

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Date:	Wed, 31 Jul 2013 17:04:14 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Timur Tabi <timur@...i.org>
CC:	Arpit Goel <B44344@...escale.com>, linux@....linux.org.uk,
	takata@...ux-m32r.org, philb@....org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	linux390@...ibm.com, David Miller <davem@...emloft.net>,
	Rob Herring <rob.herring@...xeda.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Warren <swarren@...dia.com>, john.stultz@...aro.org,
	jesper.nilsson@...s.com, gregkh@...uxfoundation.org,
	sam@...nborg.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-m32r@...linux-m32r.org, linux-m32r-ja@...linux-m32r.org,
	linux-m68k@...r.kernel.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, mattw@...eaurora.org
Subject: Re: [PATCH 2/2] Convert PowerPC macro spin_event_timeout() to architecture
 independent macro

On 07/31/13 16:44, Timur Tabi wrote:
> On Wed, Jul 31, 2013 at 2:16 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> What do you do here if jiffies aren't incrementing (i.e
>> interrupts are disabled). The time_before() check won't work
>> there and it would be nice if we were able to use this in such
>> situations. I think powerpc gets around this by reading the
>> hardware timer directly?
> I believe that jiffies is always a global variable.  It should behave
> the same on PowerPC as on other architectures.

Yes it's global but it doesn't increment while interrupts are off.

>
> The answer to your question is that you should not use
> spin_event_timeout() in interrupt context, because it yields.
>

If it yields why are we using udelay? Why not usleep_range()? It would
be useful to have a variant that worked in interrupt context and it
looked like that was almost possible.

BTW, couldn't we skip the first patch and just use usecs_to_jiffies()?

-- 
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