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

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 01/27/2015 10:08 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.

    BTW, the interrupt of the same # is still guaranteed to not occur, IIUC.

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

WBR, Sergei