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 21:19:04 Sergei Shtylyov wrote:
> Hello.
> 
> 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 ?

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

-- 
Regards,

Laurent Pinchart