gpu: ion: Add support for cached mappings that don't fault

We have found that faulting in the mappings for cached
allocations has a significant performance impact and is
only a benefit if only a small part of the buffer is
touched by the cpu (an uncommon case for software rendering).
This patch introduces a ION_FLAG_CACHED_NEEDS_SYNC
which determines whether a mapping should be created by
faulting or at mmap time.  If this flag is set,
userspace must manage the caches explictly using the SYNC ioctl.
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -164,7 +164,8 @@ static struct ion_buffer *ion_buffer_create(struct ion_heap *heap,
 		return ERR_PTR(PTR_ERR(table));
 	}
 	buffer->sg_table = table;
-	if (buffer->flags & ION_FLAG_CACHED) {
+	if (buffer->flags & ION_FLAG_CACHED &&
+	    !(buffer->flags & ION_FLAG_CACHED_NEEDS_SYNC)) {
 		for_each_sg(buffer->sg_table->sgl, sg, buffer->sg_table->nents,
 			    i) {
 			if (sg_dma_len(sg) == PAGE_SIZE)
@@ -763,7 +764,8 @@ static void ion_buffer_sync_for_device(struct ion_buffer *buffer,
 	pr_debug("%s: syncing for device %s\n", __func__,
 		 dev ? dev_name(dev) : "null");
 
-	if (!(buffer->flags & ION_FLAG_CACHED))
+	if (!(buffer->flags & ION_FLAG_CACHED) ||
+	    (buffer->flags & ION_FLAG_CACHED_NEEDS_SYNC))
 		return;
 
 	mutex_lock(&buffer->lock);
@@ -853,17 +855,21 @@ static int ion_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 		return -EINVAL;
 	}
 
-	if (buffer->flags & ION_FLAG_CACHED) {
+	if (buffer->flags & ION_FLAG_CACHED &&
+	    !(buffer->flags & ION_FLAG_CACHED_NEEDS_SYNC)) {
 		vma->vm_private_data = buffer;
 		vma->vm_ops = &ion_vma_ops;
 		ion_vm_open(vma);
-	} else {
+		return 0;
+	}
+
+	if (!(buffer->flags & ION_FLAG_CACHED))
 		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+
 	mutex_lock(&buffer->lock);
 	/* now map it to userspace */
 	ret = buffer->heap->ops->map_user(buffer->heap, buffer, vma);
 	mutex_unlock(&buffer->lock);
-	}
 
 	if (ret)
 		pr_err("%s: failure mapping buffer to userspace\n",
@@ -1021,7 +1027,9 @@ static int ion_sync_for_device(struct ion_client *client, int fd)
 		return -EINVAL;
 	}
 	buffer = dmabuf->priv;
-	ion_buffer_sync_for_device(buffer, NULL, DMA_BIDIRECTIONAL);
+
+	dma_sync_sg_for_device(NULL, buffer->sg_table->sgl,
+			       buffer->sg_table->nents, DMA_BIDIRECTIONAL);
 	dma_buf_put(dmabuf);
 	return 0;
 }

drivers/staging/android/ion/ion.h

@@ -50,6 +50,9 @@ enum ion_heap_type {
 					   cached, ion will do cache
 					   maintenance when the buffer is
 					   mapped for dma */
+#define ION_FLAG_CACHED_NEEDS_SYNC 2	/* mappings of this buffer will created
+					   at mmap time, if this is set
+					   caches must be managed manually */
 
 #ifdef __KERNEL__
 struct ion_device;