Re: [PATCH 1/3] mxc_nand: set spare size and pages per block

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Aug 11, 2010 at 03:16:34PM +0200, John Ogness wrote:
> On 2010-08-11, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> >> Your version allows a small window between request_irq() and
> >> irq_control() where on the i.MX21 there is a possibility of the
> >> interrupts being disabled twice. Namely, if an interrupt occurs
> >> before irq_control() has had a chance to disable it. IMHO it would be
> >> better to call:
> >> 
> >>     set_irq_flags(host->irq, IRQF_VALID | IRQF_NOAUTOEN);
> >> 
> >> for the i.MX21 before requesting the irq. This closes the window.
> >
> > IIRC it is not allowed to call set_irq_flags before request_irq. We
> > are changing a resource we do not own yet.
> 
> Normally, yes. But the only way the IRQF_NOAUTOEN flag can ever be
> useful is if set_irq_flags() is called before request_irq().
> 
> > I think the worst thing that could happen without this change is that
> > we get an interrupt after request_irq.
> 
> Yes. And this causes a problem on the i.MX21 because the interrupt
> handler will disable the interrupts. The irq_control() after
> request_irq() will _also_ disable the interrupts. This means the
> interrupts are disabled twice, which causes some issues on an RT kernel.
> 
> > Alternatively we could set the interrupt mask bit before requesting
> > the irq.
> 
> Yes. This would be best. But for the i.MX21 it is important that the
> interrupts are unmasked after irq_control() has disabled the interrupts.

Ok, I'll update the patches to use this approach.

Sascha

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