dmaengine: add dma_request/release_chan_linked to manage device link

In order to enforce suspend/resume ordering, this patch adds a new
API to request/release a DMA channel and create a device link
between DMA controller (DMA channel provider) and DMA client
(DMA channel consumer). This link avoids to suspend DMA before
DMA clients.

Clients who will use dma_request_chan_linked will have to
unbalanced the device link by using dma_release_chan_linked.

Change-Id: I37b69cf74b60091e2fff5447d6c623594d903737
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/155327
Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Alexandre TORGUE <alexandre.torgue@st.com>

Author: ADESTM

drivers/dma/dmaengine.c

@@ -736,6 +736,34 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
 }
 EXPORT_SYMBOL_GPL(dma_request_chan);
 
+/**
+ * dma_request_chan_linked - try to allocate an exclusive slave channel
+ * @dev:	pointer to client device structure
+ * @name:	slave channel name
+ *
+ * Returns pointer to appropriate DMA channel on success or an error pointer.
+ * Create device link between DMA channel provider and client device consumer.
+ */
+struct dma_chan *dma_request_chan_linked(struct device *dev, const char *name)
+{
+	struct dma_chan *ch = dma_request_chan(dev, name);
+	struct device *provider_dev = ch->device->dev;
+	struct device_link *link;
+
+	if (!IS_ERR_OR_NULL(ch)) {
+		link = device_link_add(dev, provider_dev, DL_FLAG_STATELESS);
+		if (!link) {
+			dev_err(provider_dev,
+				"failed to add dev link with %s\n",
+				dev_name(dev));
+			return ERR_PTR(-EINVAL);
+		}
+	}
+
+	return ch;
+}
+EXPORT_SYMBOL_GPL(dma_request_chan_linked);
+
 /**
  * dma_request_slave_channel - try to allocate an exclusive slave channel
  * @dev:	pointer to client device structure
@@ -794,6 +822,13 @@ void dma_release_channel(struct dma_chan *chan)
 }
 EXPORT_SYMBOL_GPL(dma_release_channel);
 
+void dma_release_chan_linked(struct device *dev, struct dma_chan *chan)
+{
+	device_link_remove(dev, chan->device->dev);
+	dma_release_channel(chan);
+}
+EXPORT_SYMBOL_GPL(dma_release_chan_linked);
+
 /**
  * dmaengine_get - register interest in dma_channels
  */

include/linux/dmaengine.h

@@ -1318,9 +1318,11 @@ struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
 struct dma_chan *dma_request_slave_channel(struct device *dev, const char *name);
 
 struct dma_chan *dma_request_chan(struct device *dev, const char *name);
+struct dma_chan *dma_request_chan_linked(struct device *dev, const char *name);
 struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask);
 
 void dma_release_channel(struct dma_chan *chan);
+void dma_release_chan_linked(struct device *dev, struct dma_chan *chan);
 int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
 #else
 static inline struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
@@ -1353,6 +1355,11 @@ static inline struct dma_chan *dma_request_chan(struct device *dev,
 {
 	return ERR_PTR(-ENODEV);
 }
+static inline struct dma_chan *dma_request_chan_linked(struct device *dev,
+						       const char *name)
+{
+	return ERR_PTR(-ENODEV);
+}
 static inline struct dma_chan *dma_request_chan_by_mask(
 						const dma_cap_mask_t *mask)
 {
@@ -1361,6 +1368,10 @@ static inline struct dma_chan *dma_request_chan_by_mask(
 static inline void dma_release_channel(struct dma_chan *chan)
 {
 }
+static inline void dma_release_chan_linked(struct device *dev,
+					   struct dma_chan *chan)
+{
+}
 static inline int dma_get_slave_caps(struct dma_chan *chan,
 				     struct dma_slave_caps *caps)
 {