[PATCH] ARM: Tegra: DMA: Fail safe if initialization fails

[Stephen Warren]

tegra_dma_init currently simply bails out early if any initialization fails.
This skips various data-structure initialization. In turn, this means that
tegra_dma_allocate_channel can still hand out channels. In this case, when
tegra_dma_free_channel is called, which calls tegra_dma_cancel, the walking
on ch->list will OOPS since the list's next/prev pointers may still be
NULL.

To solve this:
* Mark all possible channels as in-use before doing anything else in init.
* Only mark a channel as free once all channel-related initialization has
  completed.

This prevents allocate_channel from handing out uninitialized channels.

There is still one small hole; allocate_channel can't check the usage array
for the shared channel, since this channel is permanently marked in-use.
This could be solved using an explicit "init OK" flag that allocate_channel
could check.

Signed-off-by: Stephen Warren <swarren at nvidia.com>
---
 arch/arm/mach-tegra/dma.c |   20 ++++++++------------
 1 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c
index 2d720f2..79765ca 100644
--- a/arch/arm/mach-tegra/dma.c
+++ b/arch/arm/mach-tegra/dma.c
@@ -678,6 +678,12 @@ int __init tegra_dma_init(void)
 	void __iomem *addr;
 	struct clk *c;
 
+	memset(channel_usage, 0, sizeof(channel_usage));
+	memset(dma_channels, 0, sizeof(dma_channels));
+
+	for (i = 0; i < NV_DMA_MAX_CHANNELS; i++)
+		__set_bit(i, channel_usage);
+
 	c = clk_get_sys("tegra-dma", NULL);
 	if (IS_ERR(c)) {
 		pr_err("Unable to get clock for APB DMA\n");
@@ -696,18 +702,9 @@ int __init tegra_dma_init(void)
 	writel(0xFFFFFFFFul >> (31 - TEGRA_SYSTEM_DMA_CH_MAX),
 	       addr + APB_DMA_IRQ_MASK_SET);
 
-	memset(channel_usage, 0, sizeof(channel_usage));
-	memset(dma_channels, 0, sizeof(dma_channels));
-
-	/* Reserve all the channels we are not supposed to touch */
-	for (i = 0; i < TEGRA_SYSTEM_DMA_CH_MIN; i++)
-		__set_bit(i, channel_usage);
-
 	for (i = TEGRA_SYSTEM_DMA_CH_MIN; i <= TEGRA_SYSTEM_DMA_CH_MAX; i++) {
 		struct tegra_dma_channel *ch = &dma_channels[i];
 
-		__clear_bit(i, channel_usage);
-
 		ch->id = i;
 		snprintf(ch->name, TEGRA_DMA_NAME_SIZE, "dma_channel_%d", i);
 
@@ -726,13 +723,12 @@ int __init tegra_dma_init(void)
 			goto fail;
 		}
 		ch->irq = irq;
+
+		__clear_bit(i, channel_usage);
 	}
 	/* mark the shared channel allocated */
 	__set_bit(TEGRA_SYSTEM_DMA_CH_MIN, channel_usage);
 
-	for (i = TEGRA_SYSTEM_DMA_CH_MAX+1; i < NV_DMA_MAX_CHANNELS; i++)
-		__set_bit(i, channel_usage);
-
 	return ret;
 fail:
 	writel(0, addr + APB_DMA_GEN);
-- 
1.7.1