[PATCH] Dove: Fix irq_to_pmu()

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Sun, Nov 18, 2012 at 04:02:29PM -0500, Jason Cooper wrote:
> On Sun, Nov 18, 2012 at 08:38:15PM +0000, Russell King - ARM Linux wrote:
> > On Sun, Nov 18, 2012 at 11:00:28PM +0400, Sergei Shtylyov wrote:
> > > Hello.
> > >
> > > On 18-11-2012 20:39, Russell King - ARM Linux wrote:
> > >
> > >> PMU interrupts start at IRQ_DOVE_PMU_START, not IRQ_DOVE_PMU_START + 1.
> > >> Fix the condition.  (It may have been less likely to occur had the code
> > >> been written "if (irq >= IRQ_DOVE_PMU_START" which imho is the easier
> > >> to understand notation, and matches the normal way of thinking about
> > >> these things.)
> > >
> > >> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> > >> --
> > >
> > >    Should be "---", or somebody (you?) will have to hand edit the patch 
> > > when applying...
> > 
> > Sorry, can never remember that...
> 
> No problem, I'll handle it when I pull it in.

And there's yet another bug... this time in the kirkwood audio driver:

static irqreturn_t kirkwood_dma_irq(int irq, void *dev_id)
{
        struct kirkwood_dma_priv *prdata = dev_id;
        struct kirkwood_dma_data *priv = prdata->data;
        unsigned long mask, status, cause;   
        
        mask = readl(priv->io + KIRKWOOD_INT_MASK);
        status = readl(priv->io + KIRKWOOD_INT_CAUSE) & mask;

        cause = readl(priv->io + KIRKWOOD_ERR_CAUSE);
        if (unlikely(cause)) {
                printk(KERN_WARNING "%s: got err interrupt 0x%lx\n",
                                __func__, cause);
                writel(cause, priv->io + KIRKWOOD_ERR_CAUSE);
                return IRQ_HANDLED;
        }

What happens here if an underrun (0x20) interrupt happens?  Well, the
kernel log looks something like this:

kirkwood_dma_irq: got err interrupt 0x20
kirkwood_dma_irq: got err interrupt 0x20
kirkwood_dma_irq: got err interrupt 0x20
kirkwood_dma_irq: got err interrupt 0x20
kirkwood_dma_irq: got err interrupt 0x20
kirkwood_dma_irq: got err interrupt 0x20
...

and the system spins doing nothing but that message.  It's not because the
interrupt isn't being cleared (it's a sensible write-1-to-clear register).

If you have (frigged) orion_wdt to work, then you'll get a reset after 25s,
otherwise you'll have what appears to be a totally dead system with (due to
the log buffer rewrite) no kernel message output, no interrupts, no nothing.

It's taken a full day to track this bug down...

As for what causes the underrun, that's a different (and as yet unanswered)
question... but without the patch below which turns off the error reporting
after the first (until it's re-opened) DVD quality MPEG2 decoding fails in
less than one minute with ubuntu precise 12.10 userspace with the machine
locking solid... doesn't matter if it's software or hardware decode.

diff --git a/sound/soc/kirkwood/kirkwood-dma.c b/sound/soc/kirkwood/kirkwood-dma.c
index 690260b..26a1d36 100644
--- a/sound/soc/kirkwood/kirkwood-dma.c
+++ b/sound/soc/kirkwood/kirkwood-dma.c
@@ -73,10 +73,12 @@ static irqreturn_t kirkwood_dma_irq(int irq, void *dev_id)
 	status = readl(priv->io + KIRKWOOD_INT_CAUSE) & mask;
 
 	cause = readl(priv->io + KIRKWOOD_ERR_CAUSE);
+	cause &= readl(priv->io + KIRKWOOD_ERR_MASK);
 	if (unlikely(cause)) {
 		printk(KERN_WARNING "%s: got err interrupt 0x%lx\n",
 				__func__, cause);
 		writel(cause, priv->io + KIRKWOOD_ERR_CAUSE);
+		writel(0, priv->io + KIRKWOOD_ERR_MASK);
 		return IRQ_HANDLED;
 	}
 

Now I'm getting to the point of wondering how well tested any of this
dove/kirkwood/orion code actually is... it all looks rather insanely
fragile to me tonight.