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, add an explicit "initialized" flag, only set this once _init
has fully completed successfully, and have _allocate_channel refuse to hand
out channels if this is not set.

While at it, simplify _init:
* Remove redundant memsets
* Use bitmap_fill to mark all channels as in-use up-front, and remove
 some now-redundant bitmap initialization loops.
* Only mark a channel as free once all channel-related initialization has
 completed.

Finally, the successful exit path from _init always has ret==0, so just
hard-code that return. The error path still returns ret.

Signed-off-by: Stephen Warren <redacted>
---
v2:
* Added explicit initialized flag. I chose not to re-use the shared-channel
 bitmap entry for this purpose, since that bit needs to be marked in-use
 so that the non-shared-channel path doesn't hand out that channel.
* Removed redundant memsets
* Use bitmap_fill instead of a loop
* Hard-code success return value

 arch/arm/mach-tegra/dma.c |   23 ++++++++++-------------
 1 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c
index bd4f62a..01db832 100644
--- a/arch/arm/mach-tegra/dma.c
+++ b/arch/arm/mach-tegra/dma.c

@@ -127,8 +127,8 @@ struct tegra_dma_channel {

 #define  NV_DMA_MAX_CHANNELS  32

+static int initialized;

 static DECLARE_BITMAP(channel_usage, NV_DMA_MAX_CHANNELS);
 static struct tegra_dma_channel dma_channels[NV_DMA_MAX_CHANNELS];

@@ -352,6 +352,9 @@ struct tegra_dma_channel *tegra_dma_allocate_channel(int mode)

       int channel;
       struct tegra_dma_channel *ch = NULL;

+       if (!initialized)

+               return NULL;
+
       mutex_lock(&tegra_dma_lock);

       /* first channel is the shared channel */

@@ -678,6 +681,8 @@ int __init tegra_dma_init(void)

       void __iomem *addr;
       struct clk *c;

+       bitmap_fill(channel_usage, NV_DMA_MAX_CHANNELS);
+
       c = clk_get_sys("tegra-dma", NULL);
       if (IS_ERR(c)) {
               pr_err("Unable to get clock for APB DMA\n");

@@ -696,18 +701,9 @@ 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);

@@ -726,14 +722,15 @@ 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);
+       initialized = 1;