dmaengine: Mark dma_request_slave_channel() deprecated

New drivers should use dma_request_chan() instead
dma_request_slave_channel()

dma_request_slave_channel() is a simple wrapper for dma_request_chan()
eating up the error code for channel request failure and makes deferred
probing impossible.

Move the dma_request_slave_channel() into the header as inline function,
mark it as deprecated.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20200828110507.22407-1-peter.ujfalusi@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/dmaengine.c

@@ -871,24 +871,6 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
 }
 EXPORT_SYMBOL_GPL(dma_request_chan);
 
-/**
- * dma_request_slave_channel - 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 NULL.
- */
-struct dma_chan *dma_request_slave_channel(struct device *dev,
-					   const char *name)
-{
-	struct dma_chan *ch = dma_request_chan(dev, name);
-	if (IS_ERR(ch))
-		return NULL;
-
-	return ch;
-}
-EXPORT_SYMBOL_GPL(dma_request_slave_channel);
-
 /**
  * dma_request_chan_by_mask - allocate a channel satisfying certain capabilities
  * @mask:	capabilities that the channel must satisfy

include/linux/dmaengine.h

@@ -1472,7 +1472,6 @@ void dma_issue_pending_all(void);
 struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
 				       dma_filter_fn fn, void *fn_param,
 				       struct device_node *np);
-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_by_mask(const dma_cap_mask_t *mask);
@@ -1502,11 +1501,6 @@ static inline struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
 {
 	return NULL;
 }
-static inline struct dma_chan *dma_request_slave_channel(struct device *dev,
-							 const char *name)
-{
-	return NULL;
-}
 static inline struct dma_chan *dma_request_chan(struct device *dev,
 						const char *name)
 {
@@ -1575,6 +1569,15 @@ void dma_run_dependencies(struct dma_async_tx_descriptor *tx);
 #define dma_request_channel(mask, x, y) \
 	__dma_request_channel(&(mask), x, y, NULL)
 
+/* Deprecated, please use dma_request_chan() directly */
+static inline struct dma_chan * __deprecated
+dma_request_slave_channel(struct device *dev, const char *name)
+{
+	struct dma_chan *ch = dma_request_chan(dev, name);
+
+	return IS_ERR(ch) ? NULL : ch;
+}
+
 static inline struct dma_chan
 *dma_request_slave_channel_compat(const dma_cap_mask_t mask,
 				  dma_filter_fn fn, void *fn_param,