linux-kernel - Re: [RFC] w1: Disable irqs in critical section

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Date:	Thu, 08 Sep 2011 07:46:21 +0200
From:	Jan Weitzel <J.Weitzel@...tec.de>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC] w1: Disable irqs in critical section

Am Mittwoch, den 07.09.2011, 21:50 +0400 schrieb Evgeniy Polyakov:
> On Wed, Sep 07, 2011 at 10:48:32AM +0200, Jan Weitzel (j.weitzel@...tec.de) wrote:
> > Interrupting w1_delay in w1_read_bit results in missing the low level
> > on the w1 line and receiving "1" instead of "0".
> > Adding local_irq_save / local_irq_restore around the critical section
> 
> This means that CPU will be essentially stuck for 15 useconds for every
> bit transferred, doesn't really look like a good idea.
> 
> Are you absolutely sure that missing bit is because of timings and not
> some other bug?
> 

I trigger a gpio line after the samplepoint. I case of a wrong bit the
sample is taken after the "0 gap". The cycle time (samplt to sample)is
increased form about 80µs to 95µs. 
I did the measurement with the w1-gpio driver on a OMAP4 board.

Jan


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