Re: [PATCH 2/6] dmaengine: rcar-dmac: Fix spinlock issues in interrupt

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sergei,

On Tuesday 27 January 2015 22:01:18 Sergei Shtylyov wrote:
> On 01/27/2015 09:55 PM, Laurent Pinchart wrote:
> >> On 01/27/2015 08:25 PM, Laurent Pinchart wrote:
> >> 
> >> [...]
> >> 
> >>> Furthermore, as the driver can be used on SMP systems, the IRQ handlers
> >>> must use spin_lock_irqsave() instead of spin_lock().
> >> 
> >> Hmm, care to explain why? It's the first time I'm hearing that...
> >> This looks especially strange in the context of the current genirq code
> >> calling IRQ handlers with interrupts always disabled.
> > 
> > I should have been more precise here.
> > 
> > The DMAC has several interrupt sources than can occur simultaneously.
> > While genirq should guarantee that an interrupt will not be preempted by
> > another interrupt (including itself) on the same CPU, does it offer that
> > guarantee across CPUs in an SMP system ?
> 
> No. But spin_lock_irqsave() wouldn't help with that -- it only disables
> interrupts on the local CPU...

You're of course right. I'm not sure what I was thinking. I'll send a v2 after 
waiting for review of the other patches.

> >>> Signed-off-by: Laurent Pinchart
> >>> <laurent.pinchart+renesas@ideasonboard.com>

-- 
Regards,

Laurent Pinchart