Re: [PATCH] drm/i915: HWS must be in the mappable region for g33

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, May 19, 2014 at 07:56:11AM +0100, Chris Wilson wrote:
> This also appears to be true (but not documented as so) for gen4 and
> gen5. To generalise we force it into the low mappable region for all
> non-LLC platforms. If we locate the HWS at the top of the GTT the
> machine will hard hang during boot (fails on pnv, gm45, ilk and byt,
> but works on snb, ivb, hsw).

I take it this is the documented part?
"[DevBLB] Only:
Format = Bits 28:12 of graphics memory address (bits 31:29 MBZ)."

> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index cb6d510245b5..9576b8f57150 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1362,6 +1362,7 @@ static int init_status_page(struct intel_ring_buffer *ring)
>  	struct drm_i915_gem_object *obj;
>  
>  	if ((obj = ring->status_page.obj) == NULL) {
> +		unsigned flags;
>  		int ret;
>  
>  		obj = i915_gem_alloc_object(ring->dev, 4096);
> @@ -1374,7 +1375,10 @@ static int init_status_page(struct intel_ring_buffer *ring)
>  		if (ret)
>  			goto err_unref;
>  
> -		ret = i915_gem_obj_ggtt_pin(obj, 4096, 0);
> +		flags = 0;
> +		if (!HAS_LLC(ring->dev))
> +			flags |= PIN_MAPPABLE;

Maybe there should be a comment why we need PIN_MAPPABLE even though we
never map it?

> +		ret = i915_gem_obj_ggtt_pin(obj, 0, flags);

Why the alignment change? Well, I guess it'll end up 4k aligned anyway
since it's not tiled.

>  		if (ret) {
>  err_unref:
>  			drm_gem_object_unreference(&obj->base);
> -- 
> 2.0.0.rc2
> 
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-- 
Ville Syrjälä
Intel OTC