[Intel-gfx] [PATCH v2 1/4] drm/i915: Initialize hardware semaphore state on ring init

[Chris Wilson]

On Tue, 18 Dec 2012 19:26:18 +0200, Mika Kuoppala <mika.kuoppala at linux.intel.com> wrote:
> Hardware status page needs to have proper seqno set
> as our initial seqno can be arbitrary. If initial seqno is close
> to wrap boundary on init and i915_seqno_passed() (31bit space)
> refers to hw status page which contains zero, errorneous result
> will be returned.
> 
> v2: clear mboxes and set hws page directly instead of going
> through rings. Suggested by Chris Wilson.
> 
> v3: hws needs to be updated for all gens. Noticed by Chris
> Wilson.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=58230
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>

> -int intel_ring_handle_seqno_wrap(struct intel_ring_buffer *ring)
> +void intel_ring_init_seqno(struct intel_ring_buffer *ring, u32 seqno)
>  {
> -	int ret;
> +	struct drm_i915_private *dev_priv = ring->dev->dev_private;
>  
>  	BUG_ON(ring->outstanding_lazy_request);
>  
> -	if (INTEL_INFO(ring->dev)->gen < 6)
> -		return 0;
> -
> -	ret = __intel_ring_begin(ring, 6 * sizeof(uint32_t));
> -	if (ret)
> -		return ret;
> -
> -	/* Leaving a stale, pre-wrap seqno behind in the mboxes will result in
> -	 * post-wrap semaphore waits completing immediately. Clear them. */
> -	update_mboxes(ring, ring->signal_mbox[0]);
> -	update_mboxes(ring, ring->signal_mbox[1]);
> -	intel_ring_advance(ring);
> +	if (INTEL_INFO(ring->dev)->gen >= 6) {
> +		I915_WRITE(RING_SYNC_0(ring->mmio_base), 0);
> +		I915_WRITE(RING_SYNC_1(ring->mmio_base), 0);
> +	}
>  
> -	return 0;
> +	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);

There's yet another complication here: not all gen use the HWS. Ironlake
uses a pipecontrol write to another page -- though in principle we could
write to the HWS instead.

Any one feel like that challenge?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre