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From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
To: linux-sh@vger.kernel.org
Subject: Re: [PATCH 2/6] dmaengine: rcar-dmac: Fix spinlock issues in interrupt
Date: Tue, 27 Jan 2015 19:12:59 +0000	[thread overview]
Message-ID: <54C7E33B.9010709@cogentembedded.com> (raw)
In-Reply-To: <1422379516-1633-3-git-send-email-laurent.pinchart+renesas@ideasonboard.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


      parent reply	other threads:[~2015-01-27 19:12 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-27 17:25 [PATCH 2/6] dmaengine: rcar-dmac: Fix spinlock issues in interrupt Laurent Pinchart
2015-01-27 18:19 ` Sergei Shtylyov
2015-01-27 18:55 ` Laurent Pinchart
2015-01-27 19:01 ` Sergei Shtylyov
2015-01-27 19:08 ` Laurent Pinchart
2015-01-27 19:12 ` Sergei Shtylyov [this message]

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