[Intel-gfx] [PATCH 2/2] drm/i915: Add a test that we terminate the trimmed sgtable as expected

[Daniel Vetter]

On Mon, Dec 19, 2016 at 12:43:46PM +0000, Chris Wilson wrote:
> In commit 0c40ce130e38 ("drm/i915: Trim the object sg table"), we expect
> to copy exactly orig_st->nents across and allocate the table thusly.
> The copy loop should therefore end with the new_sg being NULL.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 4e263df2afc3..0a82cce5f731 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2316,6 +2316,7 @@ static void i915_sg_trim(struct sg_table *orig_st)
>  		/* called before being DMA mapped, no need to copy sg->dma_* */
>  		new_sg = sg_next(new_sg);
>  	}
> +	GEM_BUG_ON(new_sg); /* Should walk exactly nents and hit the end */

I wasn't sure this holds up vs. overallocation of sg tables, but the last
entry is marked and that mark seems to survive intact everywhere.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

>  
>  	sg_free_table(orig_st);
>  
> -- 
> 2.11.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch