drm/i915: Support for creating write combined type vmaps

vmaps has a provision for controlling the page protection bits, with which
we can use to control the mapping type, e.g. WB, WC, UC or even WT.
To allow the caller to choose their mapping type, we add a parameter to
i915_gem_object_pin_map - but we still only allow one vmap to be cached
per object. If the object is currently not pinned, then we recreate the
previous vmap with the new access type, but if it was pinned we report an
error. This effectively limits the access via i915_gem_object_pin_map to a
single mapping type for the lifetime of the object. Not usually a problem,
but something to be aware of when setting up the object's vmap.

We will want to vary the access type to enable WC mappings of ringbuffer
and context objects on !llc platforms, as well as other objects where we
need coherent access to the GPU's pages without going through the GTT

v2: Remove the redundant braces around pin count check and fix the marker
     in documentation (Chris)

v3:
- Add a new enum for the vmalloc mapping type & pass that as an argument to
   i915_object_pin_map. (Tvrtko)
- Use PAGE_MASK to extract or filter the mapping type info and remove a
   superfluous BUG_ON.(Tvrtko)

v4:
- Rename the enums and clean up the pin_map function. (Chris)

v5: Drop the VM_NO_GUARD, minor cosmetics.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Akash Goel <akash.goel@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471001999-17787-1-git-send-email-chris@chris-wilson.co.uk

1 files changed, 48 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index e68b4c62be88..75a57e2da86e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2077,6 +2077,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
 	list_del(&obj->global_list);
 
 	if (obj->mapping) {
+		/* low bits are ignored by is_vmalloc_addr and kmap_to_page */
 		if (is_vmalloc_addr(obj->mapping))
 			vunmap(obj->mapping);
 		else
@@ -2253,7 +2254,8 @@ i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 }
 
 /* The 'mapping' part of i915_gem_object_pin_map() below */
-static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
+static void *i915_gem_object_map(const struct drm_i915_gem_object *obj,
+				 enum i915_map_type type)
 {
 	unsigned long n_pages = obj->base.size >> PAGE_SHIFT;
 	struct sg_table *sgt = obj->pages;
@@ -2262,10 +2264,11 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
 	struct page *stack_pages[32];
 	struct page **pages = stack_pages;
 	unsigned long i = 0;
+	pgprot_t pgprot;
 	void *addr;
 
 	/* A single page can always be kmapped */
-	if (n_pages == 1)
+	if (n_pages == 1 && type == I915_MAP_WB)
 		return kmap(sg_page(sgt->sgl));
 
 	if (n_pages > ARRAY_SIZE(stack_pages)) {
@@ -2281,7 +2284,15 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
 	/* Check that we have the expected number of pages */
 	GEM_BUG_ON(i != n_pages);
 
-	addr = vmap(pages, n_pages, 0, PAGE_KERNEL);
+	switch (type) {
+	case I915_MAP_WB:
+		pgprot = PAGE_KERNEL;
+		break;
+	case I915_MAP_WC:
+		pgprot = pgprot_writecombine(PAGE_KERNEL_IO);
+		break;
+	}
+	addr = vmap(pages, n_pages, 0, pgprot);
 
 	if (pages != stack_pages)
 		drm_free_large(pages);
@@ -2290,27 +2301,54 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
 }
 
 /* get, pin, and map the pages of the object into kernel space */
-void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj)
+void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
+			      enum i915_map_type type)
 {
+	enum i915_map_type has_type;
+	bool pinned;
+	void *ptr;
 	int ret;
 
 	lockdep_assert_held(&obj->base.dev->struct_mutex);
+	GEM_BUG_ON(!i915_gem_object_has_struct_page(obj));
 
 	ret = i915_gem_object_get_pages(obj);
 	if (ret)
 		return ERR_PTR(ret);
 
 	i915_gem_object_pin_pages(obj);
+	pinned = obj->pages_pin_count > 1;
 
-	if (!obj->mapping) {
-		obj->mapping = i915_gem_object_map(obj);
-		if (!obj->mapping) {
-			i915_gem_object_unpin_pages(obj);
-			return ERR_PTR(-ENOMEM);
+	ptr = ptr_unpack_bits(obj->mapping, has_type);
+	if (ptr && has_type != type) {
+		if (pinned) {
+			ret = -EBUSY;
+			goto err;
 		}
+
+		if (is_vmalloc_addr(ptr))
+			vunmap(ptr);
+		else
+			kunmap(kmap_to_page(ptr));
+
+		ptr = obj->mapping = NULL;
 	}
 
-	return obj->mapping;
+	if (!ptr) {
+		ptr = i915_gem_object_map(obj, type);
+		if (!ptr) {
+			ret = -ENOMEM;
+			goto err;
+		}
+
+		obj->mapping = ptr_pack_bits(ptr, type);
+	}
+
+	return ptr;
+
+err:
+	i915_gem_object_unpin_pages(obj);
+	return ERR_PTR(ret);
 }
 
 static void