[PATCH 1/2] dma-heap: add device link and unlink functions

[Christian König]

This allows device drivers to specify a DMA-heap where they want their
buffers to be allocated from. This information is then exposed as
sysfs link between the device and the DMA-heap.

Useful for userspace when in need to decide from which provider to
allocate a buffer.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/dma-heap.c | 41 ++++++++++++++++++++++++++++++--------
 include/linux/dma-heap.h   | 35 ++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index c9e41e8a9e27..0f7cf713c22f 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -31,6 +31,7 @@
  * @heap_devt		heap device node
  * @list		list head connecting to list of heaps
  * @heap_cdev		heap char device
+ * @dev:		heap device in sysfs
  *
  * Represents a heap of memory from which buffers can be made.
  */
@@ -41,6 +42,7 @@ struct dma_heap {
 	dev_t heap_devt;
 	struct list_head list;
 	struct cdev heap_cdev;
+	struct device *dev;
 };
 
 static LIST_HEAD(heap_list);
@@ -49,6 +51,33 @@ static dev_t dma_heap_devt;
 static struct class *dma_heap_class;
 static DEFINE_XARRAY_ALLOC(dma_heap_minors);
 
+int dma_heap_create_device_link(struct device *dev, const char *heap)
+{
+	struct dma_heap *h;
+
+	/* check the name is valid */
+	mutex_lock(&heap_list_lock);
+	list_for_each_entry(h, &heap_list, list) {
+		if (!strcmp(h->name, heap))
+			break;
+	}
+	mutex_unlock(&heap_list_lock);
+
+	if (list_entry_is_head(h, &heap_list, list)) {
+		pr_err("dma_heap: Link to invalid heap requested %s\n", heap);
+		return -EINVAL;
+	}
+
+	return sysfs_create_link(&dev->kobj, &h->dev->kobj, DEVNAME);
+}
+EXPORT_SYMBOL(dma_heap_create_device_link);
+
+void dma_heap_remove_device_link(struct device *dev)
+{
+	sysfs_remove_link(&dev->kobj, DEVNAME);
+}
+EXPORT_SYMBOL(dma_heap_remove_device_link);
+
 static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
 				 unsigned int fd_flags,
 				 unsigned int heap_flags)
@@ -219,7 +248,6 @@ const char *dma_heap_get_name(struct dma_heap *heap)
 struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 {
 	struct dma_heap *heap, *h, *err_ret;
-	struct device *dev_ret;
 	unsigned int minor;
 	int ret;
 
@@ -261,14 +289,11 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 		goto err1;
 	}
 
-	dev_ret = device_create(dma_heap_class,
-				NULL,
-				heap->heap_devt,
-				NULL,
-				heap->name);
-	if (IS_ERR(dev_ret)) {
+	heap->dev = device_create(dma_heap_class, NULL, heap->heap_devt, NULL,
+				  heap->name);
+	if (IS_ERR(heap->dev)) {
 		pr_err("dma_heap: Unable to create device\n");
-		err_ret = ERR_CAST(dev_ret);
+		err_ret = ERR_CAST(heap->dev);
 		goto err2;
 	}
 
diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
index 0c05561cad6e..097076766496 100644
--- a/include/linux/dma-heap.h
+++ b/include/linux/dma-heap.h
@@ -65,4 +65,39 @@ const char *dma_heap_get_name(struct dma_heap *heap);
  */
 struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info);
 
+#ifdef CONFIG_DMABUF_HEAPS
+
+/**
+ * dma_heap_create_device_link() - add link between device and heap
+ * @dev: the device which should be linked to a heap
+ * @heap: name of the heap to link to
+ *
+ * Add a sysfs link between a device and a DMA-heap. This link can then be used
+ * by userspace to figure out from which DMA-heap a device wants it's buffers
+ * to be allocated.
+ */
+int dma_heap_create_device_link(struct device *dev, const char *heap);
+
+/**
+ * dma_heap_remove_device_link() - remove link between device and heap
+ * @dev: the device which should be unlinked
+ *
+ * Removes the sysfs link between the device and it's DMA-heap again when a
+ * driver is unloaded.
+ */
+void dma_heap_remove_device_link(struct device *dev);
+
+#else
+
+int dma_heap_create_device_link(struct device *dev, const char *heap)
+{
+	return 0;
+}
+
+void dma_heap_remove_device_link(struct device *dev)
+{
+}
+
+#endif
+
 #endif /* _DMA_HEAPS_H */
-- 
2.34.1