[PATCH v7 6/7] drm/i915: refactor duplicate object vmap functions (the final rework?)

[Dave Gordon <david.s.gordon@intel.com>]

This is essentially Chris Wilson's patch of a similar name, reworked on
top of Alex Dai's recent patch:
| drm/i915: Add i915_gem_object_vmap to map GEM object to virtual space

Chris' original commentary said:
| We now have two implementations for vmapping a whole object, one for
| dma-buf and one for the ringbuffer. If we couple the vmapping into
| the obj->pages lifetime, then we can reuse an obj->vmapping for both
| and at the same time couple it into the shrinker.
|
| v2: Mark the failable kmalloc() as __GFP_NOWARN (vsyrjala)
| v3: Call unpin_vmap from the right dmabuf unmapper

v4: reimplements the same functionality, but now as wrappers round the
    recently-introduced i915_gem_object_vmap_range() from Alex's patch
    mentioned above.

v5: separated from two minor but unrelated changes [Tvrtko Ursulin];
    this is the third and most substantial portion.

    Decided not to hold onto vmappings after the pin count goes to zero.
    This may reduce the benefit of Chris' scheme a bit, but does avoid
    any increased risk of exhausting kernel vmap space on 32-bit kernels
    [Tvrtko Ursulin]. Potentially, the vunmap() could be deferred until
    the put_pages() stage if a suitable notifier were written, but we're
    not doing that here. Nonetheless, the simplification of both dmabuf
    and ringbuffer code makes it worthwhile in its own right.

v6: change BUG_ON() to WARN_ON(). [Tvrtko Ursulin]

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Alex Dai <yu.dai@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         | 22 ++++++++++++++-----
 drivers/gpu/drm/i915/i915_gem.c         | 39 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_dmabuf.c  | 36 ++++--------------------------
 drivers/gpu/drm/i915/intel_ringbuffer.c |  9 ++++----
 4 files changed, 65 insertions(+), 41 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b3ae191..f1ad3b3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2172,10 +2172,7 @@ struct drm_i915_gem_object {
 		struct scatterlist *sg;
 		int last;
 	} get_page;
-
-	/* prime dma-buf support */
-	void *dma_buf_vmapping;
-	int vmapping_count;
+	void *vmapping;
 
 	/** Breadcrumb of last rendering to the buffer.
 	 * There can only be one writer, but we allow for multiple readers.
@@ -2980,7 +2977,22 @@ static inline void i915_gem_object_pin_pages(struct drm_i915_gem_object *obj)
 static inline void i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
 {
 	BUG_ON(obj->pages_pin_count == 0);
-	obj->pages_pin_count--;
+	if (--obj->pages_pin_count == 0 && obj->vmapping) {
+		/*
+		 * Releasing the vmapping here may yield less benefit than
+		 * if we kept it until put_pages(), but on the other hand
+		 * avoids issues of exhausting kernel vmappable address
+		 * space on 32-bit kernels.
+		 */
+		vunmap(obj->vmapping);
+		obj->vmapping = NULL;
+	}
+}
+
+void *__must_check i915_gem_object_pin_vmap(struct drm_i915_gem_object *obj);
+static inline void i915_gem_object_unpin_vmap(struct drm_i915_gem_object *obj)
+{
+	i915_gem_object_unpin_pages(obj);
 }
 
 void *__must_check i915_gem_object_vmap_range(struct drm_i915_gem_object *obj,
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5b6774b..4bca643 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2235,6 +2235,12 @@ static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 	ops->put_pages(obj);
 	obj->pages = NULL;
 
+	/* vmapping should have been dropped when pages_pin_count went to 0 */
+	if (WARN_ON(obj->vmapping)) {
+		vunmap(obj->vmapping);
+		obj->vmapping = NULL;
+	}
+
 	i915_gem_object_invalidate(obj);
 
 	return 0;
@@ -2464,6 +2470,39 @@ void *i915_gem_object_vmap_range(struct drm_i915_gem_object *obj,
 	return addr;
 }
 
+/**
+ * i915_gem_object_pin_vmap - pin a GEM object and map it into kernel space
+ * @obj: the GEM object to be mapped
+ *
+ * Combines the functions of get_pages(), pin_pages() and vmap_range() on
+ * the whole object.  The caller should release the mapping by calling
+ * i915_gem_object_unpin_vmap() when it is no longer required.
+ *
+ * Returns the address at which the object has been mapped, or an ERR_PTR
+ * on failure.
+ */
+void *i915_gem_object_pin_vmap(struct drm_i915_gem_object *obj)
+{
+	int ret;
+
+	ret = i915_gem_object_get_pages(obj);
+	if (ret)
+		return ERR_PTR(ret);
+
+	i915_gem_object_pin_pages(obj);
+
+	if (obj->vmapping == NULL) {
+		obj->vmapping = i915_gem_object_vmap_range(obj, 0, 0);
+
+		if (obj->vmapping == NULL) {
+			i915_gem_object_unpin_pages(obj);
+			return ERR_PTR(-ENOMEM);
+		}
+	}
+
+	return obj->vmapping;
+}
+
 void i915_vma_move_to_active(struct i915_vma *vma,
 			     struct drm_i915_gem_request *req)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index 3a5d01a..adc7b5e 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -108,40 +108,17 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 {
 	struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf);
 	struct drm_device *dev = obj->base.dev;
+	void *addr;
 	int ret;
 
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
 		return ERR_PTR(ret);
 
-	if (obj->dma_buf_vmapping) {
-		obj->vmapping_count++;
-		goto out_unlock;
-	}
-
-	ret = i915_gem_object_get_pages(obj);
-	if (ret)
-		goto err;
-
-	i915_gem_object_pin_pages(obj);
-
-	ret = -ENOMEM;
-
-	obj->dma_buf_vmapping = i915_gem_object_vmap_range(obj, 0, 0);
-
-	if (!obj->dma_buf_vmapping)
-		goto err_unpin;
-
-	obj->vmapping_count = 1;
-out_unlock:
+	addr = i915_gem_object_pin_vmap(obj);
 	mutex_unlock(&dev->struct_mutex);
-	return obj->dma_buf_vmapping;
 
-err_unpin:
-	i915_gem_object_unpin_pages(obj);
-err:
-	mutex_unlock(&dev->struct_mutex);
-	return ERR_PTR(ret);
+	return addr;
 }
 
 static void i915_gem_dmabuf_vunmap(struct dma_buf *dma_buf, void *vaddr)
@@ -150,12 +127,7 @@ static void i915_gem_dmabuf_vunmap(struct dma_buf *dma_buf, void *vaddr)
 	struct drm_device *dev = obj->base.dev;
 
 	mutex_lock(&dev->struct_mutex);
-	if (--obj->vmapping_count == 0) {
-		vunmap(obj->dma_buf_vmapping);
-		obj->dma_buf_vmapping = NULL;
-
-		i915_gem_object_unpin_pages(obj);
-	}
+	i915_gem_object_unpin_vmap(obj);
 	mutex_unlock(&dev->struct_mutex);
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 58a18e1..47f186e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2056,7 +2056,7 @@ static int init_phys_status_page(struct intel_engine_cs *ring)
 void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf)
 {
 	if (HAS_LLC(ringbuf->obj->base.dev) && !ringbuf->obj->stolen)
-		vunmap(ringbuf->virtual_start);
+		i915_gem_object_unpin_vmap(ringbuf->obj);
 	else
 		iounmap(ringbuf->virtual_start);
 	ringbuf->virtual_start = NULL;
@@ -2080,9 +2080,10 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
 		if (ret)
 			goto unpin;
 
-		ringbuf->virtual_start = i915_gem_object_vmap_range(obj, 0, 0);
-		if (ringbuf->virtual_start == NULL) {
-			ret = -ENOMEM;
+		ringbuf->virtual_start = i915_gem_object_pin_vmap(obj);
+		if (IS_ERR(ringbuf->virtual_start)) {
+			ret = PTR_ERR(ringbuf->virtual_start);
+			ringbuf->virtual_start = NULL;
 			goto unpin;
 		}
 	} else {
-- 
1.9.1

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