[PATCH v2] ARM: Tegra: DMA: Fail safe if initialization fails

[Colin Cross]

On Wed, Feb 23, 2011 at 12:06 PM, Stephen Warren <swarren at nvidia.com> wrote:
> 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 <swarren at nvidia.com>
> ---
> 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;
Use a bool, and call it something like tegra_dma_initialized to
prevent warnings if someone else forgets a static on a variable called
initialized.

>  static DEFINE_MUTEX(tegra_dma_lock);
> -
Unnecessary whitespace change

>  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)
Maybe if (WARN_ON(!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;
intialized = true

>
> -       return ret;
> +       return 0;
>  fail:
>        writel(0, addr + APB_DMA_GEN);
>        for (i = TEGRA_SYSTEM_DMA_CH_MIN; i <= TEGRA_SYSTEM_DMA_CH_MAX; i++) {
> --
> 1.7.1
>
>