[PATCH V2 6/6] drm/i915:Use the coarse ping-pong mechanism based on drm fd to dispatch the BSD command on BDW GT3

[Zhao Yakui <yakui.zhao@intel.com>]

V1->V2: Follow Daniel's comment and use the simple ping-pong mechanism.
This is only to add the support of dual BSD rings on BDW GT3 machine.
The further optimization will be considered in another patch set.

The BDW GT3 has two independent BSD rings, which can be used to process the
video commands. To be simpler, it is transparent to user-space driver/middle.
Instead the kernel driver will decide which ring is to dispatch the BSD video
command.

As every BSD ring is powerful, it is enough to dispatch the BSD video command
based on the drm fd. In such case it can play back video stream while encoding
another video stream. The coarse ping-pong mechanism is used to determine
which BSD ring is used to dispatch the BSD video command.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
---
 drivers/gpu/drm/i915/i915_dma.c            |    3 +++
 drivers/gpu/drm/i915/i915_drv.h            |    3 +++
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |   37 +++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 0b38f88..4d27cf4 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1572,6 +1572,7 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	spin_lock_init(&dev_priv->backlight_lock);
 	spin_lock_init(&dev_priv->uncore.lock);
 	spin_lock_init(&dev_priv->mm.object_stat_lock);
+	atomic_set(&dev_priv->bsd_cmd_counter, 0);
 	mutex_init(&dev_priv->dpio_lock);
 	mutex_init(&dev_priv->modeset_restore_lock);
 
@@ -1929,6 +1930,8 @@ void i915_driver_postclose(struct drm_device *dev, struct drm_file *file)
 {
 	struct drm_i915_file_private *file_priv = file->driver_priv;
 
+	if (file_priv && file_priv->bsd_ring)
+		file_priv->bsd_ring = NULL;
 	kfree(file_priv);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index ac5598c3..68e8166 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1466,6 +1466,8 @@ struct drm_i915_private {
 	struct i915_dri1_state dri1;
 	/* Old ums support infrastructure, same warning applies. */
 	struct i915_ums_state ums;
+	/* the lock for dispatch video commands on two BSD rings */
+	atomic_t bsd_cmd_counter;
 };
 
 static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
@@ -1673,6 +1675,7 @@ struct drm_i915_file_private {
 
 	struct i915_hw_context *private_default_ctx;
 	atomic_t rps_wait_boost;
+	struct  intel_ring_buffer *bsd_ring;
 };
 
 /*
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 341ec68..720ef17 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -999,6 +999,34 @@ i915_reset_gen7_sol_offsets(struct drm_device *dev,
 	return 0;
 }
 
+/**
+ * Find one BSD ring to dispatch the corresponding BSD command.
+ * The Ring ID is returned.
+ */
+static int gen8_dispatch_bsd_ring(struct drm_device *dev,
+				  struct drm_file *file)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_i915_file_private *file_priv = file->driver_priv;
+
+	/* Check whether the file_priv is using one ring */
+	if (file_priv->bsd_ring)
+		return file_priv->bsd_ring->id;
+	else {
+		/* If no, use the ping-pong mechanism to select one ring */
+		int counter, ring_id;
+		smp_mb__before_atomic_inc();
+		counter = atomic_inc_return(&dev_priv->bsd_cmd_counter);
+		if (counter % 2 == 0)
+			ring_id = VCS;
+		else
+			ring_id = VCS2;
+
+		file_priv->bsd_ring = &dev_priv->ring[ring_id];
+		return ring_id;
+	}
+}
+
 static int
 i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		       struct drm_file *file,
@@ -1043,7 +1071,14 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 
 	if ((args->flags & I915_EXEC_RING_MASK) == I915_EXEC_DEFAULT)
 		ring = &dev_priv->ring[RCS];
-	else
+	else if ((args->flags & I915_EXEC_RING_MASK) == I915_EXEC_BSD) {
+		if (HAS_BSD2(dev)) {
+			int ring_id;
+			ring_id = gen8_dispatch_bsd_ring(dev, file);
+			ring = &dev_priv->ring[ring_id];
+		} else
+			ring = &dev_priv->ring[VCS];
+	} else
 		ring = &dev_priv->ring[(args->flags & I915_EXEC_RING_MASK) - 1];
 
 	if (!intel_ring_initialized(ring)) {
-- 
1.7.10.1