Re: [PATCH] drm/i915: Preallocate request before access of the ring

[Dave Gordon <david.s.gordon@intel.com>]

On 29/04/15 17:10, yu.dai@intel.com wrote:
> From: Alex Dai <yu.dai@intel.com>
> 
> This is to avoid bad IO access caused by writing NOOP to wrap the
> ring buffer whilst ring is unpinned.
> 
> Signed-off-by: Alex Dai <yu.dai@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 732fd63..3e8fcfd 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -803,12 +803,12 @@ static int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
>  	if (ret)
>  		return ret;
>  
> -	ret = logical_ring_prepare(ringbuf, ctx, num_dwords * sizeof(uint32_t));
> +	/* Preallocate the olr before touching the ring */
> +	ret = i915_gem_request_alloc(ring, ctx);
>  	if (ret)
>  		return ret;
>  
> -	/* Preallocate the olr before touching the ring */
> -	ret = i915_gem_request_alloc(ring, ctx);
> +	ret = logical_ring_prepare(ringbuf, ctx, num_dwords * sizeof(uint32_t));
>  	if (ret)
>  		return ret;

Reviewed-by: Dave Gordon <david.s.gordon@intel.com>

with input also from John Harrison <john.c.harrison@intel.com>, who
would like to point out that this will be superceded by the Anti-OLR
patches already posted. (In that model, the request will be allocated
much earlier, and passed around explicitly rather than dangling from the
context).

.Dave.
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