[RFC/PATCH] dma: of: Make of_dma_simple_xlate match on DMA device and channel ID

[Laurent Pinchart]

When translating a DT DMA channel specifier, the most common use case is
to match the DMA channel based on the channel DMA engine and channel ID.
Modify the of_dma_simple_xlate() function to do so, simplifying the API
for DMA engine drivers.

There is no need to check the DMA cells count in the filter function as
the check is already performed by the caller in of_dma_get_controller().

Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
 drivers/dma/of-dma.c   | 39 +++++++++++++++++++++++++++++++--------
 drivers/dma/omap-dma.c |  8 +-------
 include/linux/of_dma.h |  5 -----
 3 files changed, 32 insertions(+), 20 deletions(-)

I've implemented this function while working on a DMA engine driver, and
realized that it wasn't specific to my driver at all. As I'm new to the DMA
engine API, I'd appreciate feedback on whether this change makes sense, or if
I should instead keep the existing of_dma_simple_xlate() function and create a
separate simple xlate helper.

diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
index 7aa0864..702a45d 100644
--- a/drivers/dma/of-dma.c
+++ b/drivers/dma/of-dma.c
@@ -202,6 +202,27 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
 	return NULL;
 }
 
+struct of_dma_filter_args {
+	struct dma_device *device;
+	unsigned int chan_id;
+};
+
+/**
+ * of_dma_simple_xlate_filter - Channel filter function for of_dma_simple_xlate
+ * @dma_chan:	pointer to candidate DMA channel
+ * @param:	pointer to filter parameter
+ *
+ * Filter out candidate DMA channels that don't match the channel ID or DMA
+ * engine device passed as arguments.
+ */
+static bool of_dma_simple_xlate_filter(struct dma_chan *chan, void *param)
+{
+	struct of_dma_filter_args *fargs = param;
+
+	return (chan->device == fargs->device) &&
+	       (chan->chan_id == fargs->chan_id);
+}
+
 /**
  * of_dma_simple_xlate - Simple DMA engine translation function
  * @dma_spec:	pointer to DMA specifier as found in the device tree
@@ -216,16 +237,18 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
 struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
 						struct of_dma *ofdma)
 {
-	int count = dma_spec->args_count;
-	struct of_dma_filter_info *info = ofdma->of_dma_data;
+	struct dma_device *dev = ofdma->of_dma_data;
+	struct of_dma_filter_args fargs;
+	dma_cap_mask_t cap;
 
-	if (!info || !info->filter_fn)
-		return NULL;
+	/* There's no need to specify matching caps as we're going to match a
+	 * specific DMA channel anyway.
+	 */
+	dma_cap_zero(cap);
 
-	if (count != 1)
-		return NULL;
+	fargs.device = dev;
+	fargs.chan_id = dma_spec->args[0];
 
-	return dma_request_channel(info->dma_cap, info->filter_fn,
-			&dma_spec->args[0]);
+	return dma_request_channel(cap, of_dma_simple_xlate_filter, &fargs);
 }
 EXPORT_SYMBOL_GPL(of_dma_simple_xlate);
diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
index ec3fc4f..7e7ff06 100644
--- a/drivers/dma/omap-dma.c
+++ b/drivers/dma/omap-dma.c
@@ -69,10 +69,6 @@ static const unsigned es_bytes[] = {
 	[OMAP_DMA_DATA_TYPE_S32] = 4,
 };
 
-static struct of_dma_filter_info omap_dma_info = {
-	.filter_fn = omap_dma_filter_fn,
-};
-
 static inline struct omap_dmadev *to_omap_dma_dev(struct dma_device *d)
 {
 	return container_of(d, struct omap_dmadev, ddev);
@@ -641,11 +637,9 @@ static int omap_dma_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, od);
 
 	if (pdev->dev.of_node) {
-		omap_dma_info.dma_cap = od->ddev.cap_mask;
-
 		/* Device-tree DMA controller registration */
 		rc = of_dma_controller_register(pdev->dev.of_node,
-				of_dma_simple_xlate, &omap_dma_info);
+				of_dma_simple_xlate, &od->ddev);
 		if (rc) {
 			pr_warn("OMAP-DMA: failed to register DMA controller\n");
 			dma_async_device_unregister(&od->ddev);
diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
index 364dda7..3c0d9ac 100644
--- a/include/linux/of_dma.h
+++ b/include/linux/of_dma.h
@@ -27,11 +27,6 @@ struct of_dma {
 	void			*of_dma_data;
 };
 
-struct of_dma_filter_info {
-	dma_cap_mask_t	dma_cap;
-	dma_filter_fn	filter_fn;
-};
-
 #ifdef CONFIG_OF
 extern int of_dma_controller_register(struct device_node *np,
 		struct dma_chan *(*of_dma_xlate)
-- 
Regards,

Laurent Pinchart

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