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

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Date:	Wed, 21 Mar 2012 21:32:31 +0200
From:	Mika Westerberg <mika.westerberg@....fi>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
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 Wed, Mar 21, 2012 at 12:12:11PM -0500, H Hartley Sweeten wrote:
> On Tuesday, March 20, 2012 1:09 AM, Rafal Prylowski wrote:
> >
> > Implement double buffering for M2M DMA channels.
> >
> > Signed-off-by: Rafal Prylowski <prylowski@...asoft.pl>
> 
> Hmm... This isn't working on my ep9307 board...
> 
> When the system boots I get stormed with messages:
> 
> dma dma1chan0: unknown interrupt!
> dma dma1chan0: unknown interrupt!
> dma dma1chan0: unknown interrupt!
> dma dma1chan1: unknown interrupt!
> dma dma1chan1: unknown interrupt!
> dma dma1chan1: unknown interrupt!
> dma dma1chan0: unknown interrupt!
> dma dma1chan0: unknown interrupt!
> dma dma1chan1: unknown interrupt!
> 
> Note, I have use_dma set for the ep93xx_spi driver and am using mmc_spi.
> 
> Also note, without your patch I also get a couple messages:
> 
> dma dma1chan1: got interrupt while active list is empty
> 
> But, the mmc card is working fine. I haven't tracked down why I get these
> yet. Mika, any ideas?

I've noticed the same. But they also happen without this patch applied. I've
tracked it down to MULTI_IRQ_HANDLER support patches for ARM vic but not sure
what might be wrong there (or is the ep93xx_dma driver behaving badly). I
noticed that when we get that 'got interrupt while active list is empty' we
don't have any interrupts set in the M2M_INTERRUPT register but we still got
an interrupt.. weird.

Below is a workaround I've been using lately but it certainly is a hack and we
should figure out what is the root cause for this.

diff --git a/arch/arm/common/vic.c b/arch/arm/common/vic.c
index dcb004a..cb6b49a 100644
--- a/arch/arm/common/vic.c
+++ b/arch/arm/common/vic.c
@@ -441,11 +441,9 @@ static int handle_one_vic(struct vic_device *vic, struct pt_regs *regs)
 	u32 stat, irq;
 	int handled = 0;
 
-	stat = readl_relaxed(vic->base + VIC_IRQ_STATUS);
-	while (stat) {
+	while ((stat = readl_relaxed(vic->base + VIC_IRQ_STATUS))) {
 		irq = ffs(stat) - 1;
 		handle_IRQ(irq_domain_to_irq(&vic->domain, irq), regs);
-		stat &= ~(1 << irq);
 		handled = 1;
 	}
 
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