Re: [PATCH/RFC] i2c: rcar: Fix order of restart and clear status

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

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On Sat, Mar 07, 2015 at 11:33:49AM +0100, Wolfram Sang wrote:
> On Fri, Mar 06, 2015 at 11:05:31PM +0100, Wolfram Sang wrote:
> > 
> > > I asked Kataoka-san about this and his response was as follows:
> > 
> > Thanks, Simon!
> > 
> > > If system(CPU) is busy, the driver can't clear the status register soon
> > > after kicking start.
> > > 
> > > If sequence of first start is as follows, there is a problem.
> > > Because H/W starts by 1.
> > > But sequence of re-start is as follows, there is no problem.
> > > Because H/W starts by 2.
> > > 
> > >   1. Issue START condition by ESG bit of ICMCR register.
> > >                   <--- If there is too much time, H/W finish transmitting
> > >                        and set status in status register.
> > >   2. Clear interrupt status (ICMSR).
> > >   3. Open interrupt mask.
> > >   4. Wait interrupt.
> > >                   <--- If status is cleared, interrupt does not occur.
> > 
> > I understand. I'll add this explanation to the patch and apply it soon.
> 
> Sorry, another question came up while applying:
> 
> How can this interruption happen? The function is called in a
> spin_lock_irqsave protected area. Is this an RT_PREEMPT related issue?
> Am I missing something?

Hi,

any news on this one?

Kind regards,

   Wolfram


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