[PATCH v2] arm/tegra: use APB DMA for accessing APB devices

[Stephen Warren]

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 at nvidia.com>

-- 
nvpublic