linux-kernel - RE: [PATCH] ep93xx: Implement double buffering for M2M DMA channels

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Message-ID: <ADE657CA350FB648AAC2C43247A983F0020696D48E1A@AUSP01VMBX24.collaborationhost.net>
Date:	Thu, 22 Mar 2012 18:56:30 -0500
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	Mika Westerberg <mika.westerberg@....fi>
CC:	Rafal Prylowski <prylowski@...asoft.pl>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"rmallon@...il.com" <rmallon@...il.com>
Subject: RE: [PATCH] ep93xx: Implement double buffering for M2M DMA channels

On Thursday, March 22, 2012 1:04 PM, Mika Westerberg wrote:
> On Thu, Mar 22, 2012 at 01:52:52PM -0500, H Hartley Sweeten wrote:
>
>> I hacked this back to the handle_one_vic function. It looks like every time
>> I get the message above the stat read in that function shows an active
>> interrupt for DMAM2M0 (the dma rx channel) and DMAM2M1 (the dma
>> tx channel). Because of the way handle_one_vic processes the irq's, the
>> DMAM2M0 interrupt gets handled first. When it's done it must be clearing
>> the DMAM2M1 interrupt automatically for some reason. So, when it's
>> handled there is no interrupt pending so we get the message.
>> 
>> The "cleanest" fix I can think of is the following patch.  This is against
>> linux-next.
>
> I can't figure out any better fix unless we move ep93xx back to use
> !MULTI_IRQ_HANDLER which obviously is not good thing to do.

Mika,

I wonder if the spurious interrupts were the real problem behind what
was causing the Oops that prompted your patch:

dma/ep93xx_dma: prevent ep93xx_dma_tasklet() to reference an empty list

???

Hartley

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