drm/i915: use PIPE_CONTROL instruction on Ironlake and Sandy Bridge

Since 965, the hardware has supported the PIPE_CONTROL command, which
provides fine grained GPU cache flushing control.  On recent chipsets,
this instruction is required for reliable interrupt and sequence number
reporting in the driver.

So add support for this instruction, including workarounds, on Ironlake
and Sandy Bridge hardware.

https://bugs.freedesktop.org/show_bug.cgi?id=27108

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -236,11 +236,14 @@ typedef struct drm_i915_private {
 
 	drm_dma_handle_t *status_page_dmah;
 	void *hw_status_page;
+	void *seqno_page;
 	dma_addr_t dma_status_page;
 	uint32_t counter;
 	unsigned int status_gfx_addr;
+	unsigned int seqno_gfx_addr;
 	drm_local_map_t hws_map;
 	struct drm_gem_object *hws_obj;
+	struct drm_gem_object *seqno_obj;
 	struct drm_gem_object *pwrctx;
 
 	struct resource mch_res;
@@ -1139,6 +1142,7 @@ extern int i915_wait_ring(struct drm_device * dev, int n, const char *caller);
 
 #define HAS_PCH_SPLIT(dev) (IS_IRONLAKE(dev) ||	\
 			    IS_GEN6(dev))
+#define HAS_PIPE_CONTROL(dev) (IS_IRONLAKE(dev) || IS_GEN6(dev))
 
 #define PRIMARY_RINGBUFFER_SIZE         (128*1024)