Re: [PATCH 2/4] drm/i915: Poison the request before emitting commands

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> If we poison the request before we emit commands, it should be easier to
> spot when we execute an uninitialised request.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=100144
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 8c874996c617..1ec98851a621 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1693,6 +1693,7 @@ u32 *intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
>  
>  	GEM_BUG_ON(ring->emit > ring->size - bytes);
>  	cs = ring->vaddr + ring->emit;
> +	GEM_DEBUG_EXEC(memset(cs, POISON_INUSE, bytes));

Will more modern hardware just skipover these? If so
then perhaps more advanced solution would be to fill with bb
start into the previous address to get a guaranteed
hang on the spot.

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

>  	ring->emit += bytes;
>  	ring->space -= bytes;
>  	GEM_BUG_ON(ring->space < 0);
> -- 
> 2.11.0
>
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