[PATCH 04/10] drm/i915: Clearing buffer objects via CPU/GTT

[ankitprasad.r.sharma@intel.com]

From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>

This patch adds support for clearing buffer objects via CPU/GTT. This
is particularly useful for clearing out the non shmem backed objects.
Currently intend to use this only for buffers allocated from stolen
region.

v2: Added kernel doc for i915_gem_clear_object(), corrected/removed
variable assignments (Tvrtko)

v3: Map object page by page to the gtt if the pinning of the whole object
to the ggtt fails, Corrected function name (Chris)

v4: Clear the buffer page by page, and not map the whole object in the gtt
aperture. Use i915 wrapper function in place of drm_mm_insert_node_in_range.

v5: Use renamed wrapper function for drm_mm_insert_node_in_range,
updated barrier positioning (Chris)

v6: Use PAGE_SIZE instead of 4096, use get_pages call before pinning pages
(Tvrtko)

v7: Fixed the onion (undo operation in reverse order) (Chris)

Testcase: igt/gem_stolen

Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/i915_gem.c | 47 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e4c25c6..1122e1b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2938,6 +2938,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
 				    int *needs_clflush);
 
 int __must_check i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
+int i915_gem_object_clear(struct drm_i915_gem_object *obj);
 
 static inline int __sg_page_count(struct scatterlist *sg)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 49a03f2..1aa4fc9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5405,3 +5405,50 @@ fail:
 	drm_gem_object_unreference(&obj->base);
 	return ERR_PTR(ret);
 }
+
+/**
+ * i915_gem_object_clear() - Clear buffer object via CPU/GTT
+ * @obj: Buffer object to be cleared
+ *
+ * Return: 0 - success, non-zero - failure
+ */
+int i915_gem_object_clear(struct drm_i915_gem_object *obj)
+{
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
+	struct drm_mm_node node;
+	char __iomem *base;
+	uint64_t size = obj->base.size;
+	int ret, i;
+
+	lockdep_assert_held(&obj->base.dev->struct_mutex);
+	ret = insert_mappable_node(i915, &node, PAGE_SIZE);
+	if (ret)
+		return ret;
+
+	ret = i915_gem_object_get_pages(obj);
+	if (ret)
+		goto err_remove_node;
+
+	i915_gem_object_pin_pages(obj);
+	base = io_mapping_map_wc(i915->gtt.mappable, node.start);
+
+	for (i = 0; i < size/PAGE_SIZE; i++) {
+		i915->gtt.base.insert_page(&i915->gtt.base,
+					   i915_gem_object_get_dma_address(obj, i),
+					   node.start,
+					   I915_CACHE_NONE, 0);
+		wmb(); /* flush modifications to the GGTT (insert_page) */
+		memset_io(base, 0, PAGE_SIZE);
+		wmb(); /* flush the write before we modify the GGTT */
+	}
+
+	io_mapping_unmap(base);
+	i915->gtt.base.clear_range(&i915->gtt.base,
+			node.start, node.size,
+			true);
+	i915_gem_object_unpin_pages(obj);
+
+err_remove_node:
+	remove_mappable_node(&node);
+	return ret;
+}
-- 
1.9.1

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