drm/i915: enable to read CSB and CSB write pointer from HWSP in GVT-g VM

Let GVT-g VM read the CSB and CSB write pointer from virtual HWSP, not all
the host support this feature, need to check the BIT(3) of caps in PVINFO.

v3 : Remove unnecessary comments.
v4 : Separate VM enable patch with GVT-g implementation patch due to code
dependency.
v5 : Use inline for GVT virtual HWSP caps check function.
v6 : Comments refine.

Signed-off-by: Weinan Li <weinan.z.li@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1508039725-1066-1-git-send-email-weinan.z.li@intel.com

drivers/gpu/drm/i915/i915_pvinfo.h

@@ -53,6 +53,7 @@ enum vgt_g2v_type {
  * VGT capabilities type
  */
 #define VGT_CAPS_FULL_48BIT_PPGTT	BIT(2)
+#define VGT_CAPS_HWSP_EMULATION		BIT(3)
 
 struct vgt_if {
 	u64 magic;		/* VGT_MAGIC */

drivers/gpu/drm/i915/i915_vgpu.h

@@ -30,6 +30,12 @@ void i915_check_vgpu(struct drm_i915_private *dev_priv);
 
 bool intel_vgpu_has_full_48bit_ppgtt(struct drm_i915_private *dev_priv);
 
+static inline bool
+intel_vgpu_has_hwsp_emulation(struct drm_i915_private *dev_priv)
+{
+	return dev_priv->vgpu.caps & VGT_CAPS_HWSP_EMULATION;
+}
+
 int intel_vgt_balloon(struct drm_i915_private *dev_priv);
 void intel_vgt_deballoon(struct drm_i915_private *dev_priv);
 

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -25,6 +25,7 @@
 #include <drm/drm_print.h>
 
 #include "i915_drv.h"
+#include "i915_vgpu.h"
 #include "intel_ringbuffer.h"
 #include "intel_lrc.h"
 
@@ -386,10 +387,6 @@ static void intel_engine_init_timeline(struct intel_engine_cs *engine)
 
 static bool csb_force_mmio(struct drm_i915_private *i915)
 {
-	/* GVT emulation depends upon intercepting CSB mmio */
-	if (intel_vgpu_active(i915))
-		return true;
-
 	/*
 	 * IOMMU adds unpredictable latency causing the CSB write (from the
 	 * GPU into the HWSP) to only be visible some time after the interrupt
@@ -398,6 +395,10 @@ static bool csb_force_mmio(struct drm_i915_private *i915)
 	if (intel_vtd_active())
 		return true;
 
+	/* Older GVT emulation depends upon intercepting CSB mmio */
+	if (intel_vgpu_active(i915) && !intel_vgpu_has_hwsp_emulation(i915))
+		return true;
+
 	return false;
 }
 

drivers/gpu/drm/i915/intel_lrc.c

@@ -793,7 +793,6 @@ static void intel_lrc_irq_handler(unsigned long data)
 			&engine->status_page.page_addr[I915_HWS_CSB_BUF0_INDEX];
 		unsigned int head, tail;
 
-		/* However GVT emulation depends upon intercepting CSB mmio */
 		if (unlikely(execlists->csb_use_mmio)) {
 			buf = (u32 * __force)
 				(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0)));