dmaengine: add interface of dma_get_slave_channel

Suggested by Arnd, add dma_get_slave_channel interface
Dma host driver could get specific channel specificied by request line, rather than filter.

host example:
static struct dma_chan *xx_of_dma_simple_xlate(struct of_phandle_args *dma_spec,
		struct of_dma *ofdma)
{
	struct xx_dma_dev *d = ofdma->of_dma_data;
	unsigned int request = dma_spec->args[0];

	if (request > d->dma_requests)
		return NULL;

	return dma_get_slave_channel(&(d->chans[request].vc.chan));
}

probe:
of_dma_controller_register((&op->dev)->of_node, xx_of_dma_simple_xlate, d);

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9e56745f87bf..5932ab164ace 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -504,6 +504,32 @@ static struct dma_chan *private_candidate(const dma_cap_mask_t *mask,
 }
 
 /**
+ * dma_request_channel - try to get specific channel exclusively
+ * @chan: target channel
+ */
+struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
+{
+        int err = -EBUSY;
+
+        /* lock against __dma_request_channel */
+        mutex_lock(&dma_list_mutex);
+
+        if (chan->client_count == 0)
+                err = dma_chan_get(chan);
+        else
+                chan = NULL;
+
+        mutex_unlock(&dma_list_mutex);
+
+        if (err)
+                pr_debug("%s: failed to get %s: (%d)\n",
+                        __func__, dma_chan_name(chan), err);
+
+        return chan;
+}
+EXPORT_SYMBOL_GPL(dma_get_slave_channel);
+
+/**
  * dma_request_channel - try to allocate an exclusive channel
  * @mask: capabilities that the channel must satisfy
  * @fn: optional callback to disposition available channels