Olof Johansson wrote at Wednesday, January 04, 2012 10:49 PM:
> Tegra2 hangs if APB registers are accessed from the cpu during an
> apb dma operation. The workaround is to use apb dma to read/write the
> registers instead.
...
> diff --git a/arch/arm/mach-tegra/apbio.c b/arch/arm/mach-tegra/apbio.c
...
> +u32 tegra_apb_readl(unsigned long offset)
...
> + INIT_COMPLETION(tegra_apb_wait);
> +
> + tegra_dma_enqueue_req(tegra_apb_dma, &req);
> +
> + ret = wait_for_completion_timeout(&tegra_apb_wait,
> + msecs_to_jiffies(50));
> +
> + if (WARN(ret == 0, "apb read dma timed out")) {
> + *(u32 *)tegra_apb_bb = 0;
> + tegra_dma_dequeue_req(tegra_apb_dma, &req);
I think you need to swap those last two lines to make absolutely sure
that the timeout handling doesn't race with an actual DMA completion.
Otherwise,
Acked-by: Stephen Warren <swarren@xxxxxxxxxx>
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