drm/i915/execlists: Unify CSB access pointers

Following the removal of the last workarounds, the only CSB mmio access
is for the old vGPU interface. The mmio registers presented by vGPU do
not require forcewake and can be treated as ordinary volatile memory,
i.e. they behave just like the HWSP access just at a different location.
We can reduce the CSB access to a set of read/write/buffer pointers and
treat the various paths identically and not worry about forcewake.
(Forcewake is nightmare for worstcase latency, and we want to process
this all with irqsoff -- no latency allowed!)

v2: Comments, comments, comments. Well, 2 bonus comments.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628201211.13837-5-chris@chris-wilson.co.uk

1 files changed, 17 insertions, 6 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 78f01a35823a..25792889dbf4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -300,24 +300,35 @@ struct intel_engine_execlists {
 	struct rb_node *first;
 
 	/**
-	 * @fw_domains: forcewake domains for irq tasklet
+	 * @csb_read: control register for Context Switch buffer
+	 *
+	 * Note this register is always in mmio.
 	 */
-	unsigned int fw_domains;
+	u32 __iomem *csb_read;
 
 	/**
-	 * @csb_head: context status buffer head
+	 * @csb_write: control register for Context Switch buffer
+	 *
+	 * Note this register may be either mmio or HWSP shadow.
 	 */
-	unsigned int csb_head;
+	u32 *csb_write;
 
 	/**
-	 * @csb_use_mmio: access csb through mmio, instead of hwsp
+	 * @csb_status: status array for Context Switch buffer
+	 *
+	 * Note these register may be either mmio or HWSP shadow.
 	 */
-	bool csb_use_mmio;
+	u32 *csb_status;
 
 	/**
 	 * @preempt_complete_status: expected CSB upon completing preemption
 	 */
 	u32 preempt_complete_status;
+
+	/**
+	 * @csb_head: context status buffer head
+	 */
+	u8 csb_head;
 };
 
 #define INTEL_ENGINE_CS_MAX_NAME 8