[PATCH v2] arm/tegra: use APB DMA for accessing APB devices
From: Stephen Warren <hidden>
Date: 2012-01-05 22:07:32
Also in:
linux-tegra
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.
...
quoted hunk ↗ jump to hunk
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 <redacted> -- nvpublic