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    SubjectRe: [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@metasoft.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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