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

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.

...

...

+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 <redacted>

-- 
nvpublic