[PATCH 3/3] dma-fence: Introduce drm_fence_set_error() helper

[Sumit Semwal]

Hi Chris,

On 4 January 2017 at 19:42, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> The dma_fence.error field (formerly known as dma_fence.status) is an
> optional field that may be set by drivers before calling
> dma_fence_signal(). The field can be used to indicate that the fence was
> completed in err rather than with success, and is visible to other
> consumers of the fence and to userspace via sync_file.
>
> This patch renames the field from status to error so that its meaning is
> hopefully more clear (and distinct from dma_fence_get_status() which is
> a composite between the error state and signal state) and adds a helper
> that validates the preconditions of when it is suitable to adjust the
> error field.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/dma-buf/dma-fence.c |  2 +-
>  include/linux/dma-fence.h   | 30 +++++++++++++++++++++++++-----
>  2 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 7d936d19e659..ee82f36cb25e 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -559,7 +559,7 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
>         fence->context = context;
>         fence->seqno = seqno;
>         fence->flags = 0UL;
> -       fence->status = 0;
> +       fence->error = 0;
>
>         trace_dma_fence_init(fence);
>  }
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 19f7af905182..6048fa404e57 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -47,7 +47,7 @@ struct dma_fence_cb;
>   * can be compared to decide which fence would be signaled later.
>   * @flags: A mask of DMA_FENCE_FLAG_* defined below
>   * @timestamp: Timestamp when the fence was signaled.
> - * @status: Optional, only valid if < 0, must be set before calling
> + * @error: Optional, only valid if < 0, must be set before calling
>   * dma_fence_signal, indicates that the fence has completed with an error.
>   *
>   * the flags member must be manipulated and read using the appropriate
> @@ -79,7 +79,7 @@ struct dma_fence {
>         unsigned seqno;
>         unsigned long flags;
>         ktime_t timestamp;
> -       int status;
> +       int error;
>  };
>
>  enum dma_fence_flag_bits {
> @@ -133,7 +133,7 @@ struct dma_fence_cb {
>   * or some failure occurred that made it impossible to enable
>   * signaling. True indicates successful enabling.
>   *
> - * fence->status may be set in enable_signaling, but only when false is
> + * fence->error may be set in enable_signaling, but only when false is
>   * returned.
>   *
>   * Calling dma_fence_signal before enable_signaling is called allows
> @@ -145,7 +145,7 @@ struct dma_fence_cb {
>   * the second time will be a noop since it was already signaled.
>   *
>   * Notes on signaled:
> - * May set fence->status if returning true.
> + * May set fence->error if returning true.
>   *
>   * Notes on wait:
>   * Must not be NULL, set to dma_fence_default_wait for default implementation.
> @@ -395,13 +395,33 @@ static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
>  static inline int dma_fence_get_status_locked(struct dma_fence *fence)
>  {
>         if (dma_fence_is_signaled_locked(fence))
> -               return fence->status < 0 ? fence->status : 1;
> +               return fence->error ?: 1;
>         else
>                 return 0;
>  }
>
>  int dma_fence_get_status(struct dma_fence *fence);
>
> +/**
> + * dma_fence_set_error - flag an error condition on the fence
> + * @fence: [in]        the dma_fence
> + * @error: [in]        the error to store
> + *
> + * Drivers can supply an optional error status condition before they signal
> + * the fence, to indicate that the fence was completed due to an error
> + * rather than success. This must be set before signaling (so that the value
> + * is visible before any waiters on the signal callback are woken). This
> + * helper exists to help catching erroneous setting of #dma_fence.error.
> + */
> +static inline void dma_fence_set_error(struct dma_fence *fence,
> +                                      int error)
> +{
> +       BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
> +       BUG_ON(error >= 0 || error < -MAX_ERRNO);
> +
> +       fence->error = error;
> +}
Sorry I missed this earlier, but are you sure you want to use a BUG_ON
here, and not a WARN_ON?
> +
>  signed long dma_fence_wait_timeout(struct dma_fence *,
>                                    bool intr, signed long timeout);
>  signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
> --
> 2.11.0
>
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Best,
Sumit.