[Intel-gfx] [PATCH v2 2/2] drm/i915: enable to read CSB and CSB write pointer from HWSP in GVT-g VM

[Weinan Li]

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.

Signed-off-by: Weinan Li <weinan.z.li at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_vgpu.c       |  5 +++++
 drivers/gpu/drm/i915/i915_vgpu.h       |  1 +
 drivers/gpu/drm/i915/intel_engine_cs.c | 11 +++++++----
 drivers/gpu/drm/i915/intel_lrc.c       |  7 ++++++-
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vgpu.c b/drivers/gpu/drm/i915/i915_vgpu.c
index 5fe9f3f..6f713c5 100644
--- a/drivers/gpu/drm/i915/i915_vgpu.c
+++ b/drivers/gpu/drm/i915/i915_vgpu.c
@@ -86,6 +86,11 @@ bool intel_vgpu_has_full_48bit_ppgtt(struct drm_i915_private *dev_priv)
 	return dev_priv->vgpu.caps & VGT_CAPS_FULL_48BIT_PPGTT;
 }
 
+bool intel_vgpu_has_hwsp_emulation(struct drm_i915_private *dev_priv)
+{
+	return dev_priv->vgpu.caps & VGT_CAPS_HWSP_EMULATION;
+}
+
 struct _balloon_info_ {
 	/*
 	 * There are up to 2 regions per mappable/unmappable graphic
diff --git a/drivers/gpu/drm/i915/i915_vgpu.h b/drivers/gpu/drm/i915/i915_vgpu.h
index b72bd29..cec0ec1 100644
--- a/drivers/gpu/drm/i915/i915_vgpu.h
+++ b/drivers/gpu/drm/i915/i915_vgpu.h
@@ -29,6 +29,7 @@
 void i915_check_vgpu(struct drm_i915_private *dev_priv);
 
 bool intel_vgpu_has_full_48bit_ppgtt(struct drm_i915_private *dev_priv);
+bool intel_vgpu_has_hwsp_emulation(struct drm_i915_private *dev_priv);
 
 int intel_vgt_balloon(struct drm_i915_private *dev_priv);
 void intel_vgt_deballoon(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index a28e2a8..58945ef 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -23,6 +23,7 @@
  */
 
 #include "i915_drv.h"
+#include "i915_vgpu.h"
 #include "intel_ringbuffer.h"
 #include "intel_lrc.h"
 
@@ -384,10 +385,6 @@ 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
@@ -396,6 +393,12 @@ static bool csb_force_mmio(struct drm_i915_private *i915)
 	if (intel_vtd_active())
 		return true;
 
+	/* GVT emulation depends upon host kernel implementation, check
+	 * support capbility by reading PV INFO before access HWSP.
+	 */
+	if (intel_vgpu_active(i915) && !intel_vgpu_has_hwsp_emulation(i915))
+		return true;
+
 	return false;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7d6da13..2313d0a 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -722,7 +722,12 @@ 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 */
+		/* However GVT-g emulation depends upon host kernel
+		 * implementation, need to check support capbility by reading PV
+		 * INFO before access HWSP. Beside from this, another special
+		 * configuration may also need to force use mmio, like IOMMU
+		 * enabled.
+		 */
 		if (unlikely(execlists->csb_use_mmio)) {
 			buf = (u32 * __force)
 				(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0)));
-- 
1.9.1