[PATCH/RFC v4 09/15] DMA: shdma: support referencing specific DMACs within a multiplexer in DT

[Guennadi Liakhovetski]

Currently shdma DT nodes have to be placed under a multiplexer node. DMA
slave DT nodes then use that multiplexer's phandle in their "dmas"
properties. However, sometimes it can be necessary to let DMA slaves only
use a specific DMAC instance. In this case it would be logical to just use
the respective phandle in that slave's "dmas" property. For this to work
the referenced DMAC has to register a struct of_dma instance, which isn't
presently done. Instead the driver currently only registers one struct
of_dma for the multiplexer. This patch adds support for such
configurations. To enable this option a "#dma-cells" property also must be
added to the respective DMAC DT node.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@xxxxxxxxx>
---

As mentioned in the cover letter patch, this is an RFC. We are certain,
that we want to be able to reference specific DMACs within multiplexers.
However, with the current implementation this cannot work, because single
DMAC DT nodes don't have of_dma objects associated with them, currently
there is only one such object per multiplexer. The proposal is to
implement such direct referencing by adding a "#dma-cells" property to
respective DT nodes, in which case an of_dma object will be allocated for
them too.

 Documentation/devicetree/bindings/dma/shdma.txt |   16 ++++++
 drivers/dma/sh/shdma.h                          |    7 +++
 drivers/dma/sh/shdmac.c                         |   66 +++++++++++++++++++++++
 3 files changed, 89 insertions(+), 0 deletions(-)

diff --git a/Documentation/devicetree/bindings/dma/shdma.txt b/Documentation/devicetree/bindings/dma/shdma.txt
index 6b015d6..aeed9b8 100644
--- a/Documentation/devicetree/bindings/dma/shdma.txt
+++ b/Documentation/devicetree/bindings/dma/shdma.txt
@@ -27,6 +27,22 @@ Required properties:
 		"renesas,shdma-r8a7740" for the DMACs (not RTDMAC) on r8a7740
 		"renesas,shdma-sh73a0" for the DMACs on sh73a0
 
+Optional properties:
+- #dma-cells:	this property is only needed in one specific case: if DMA slaves
+		have to be able to request channels specifically from this DMAC,
+		not from anyone from the multiplexer. In such a case the board
+		.dts file can contain code, similar to this:
+
+&dma1 {
+	#dma-cells = <1>;
+};
+
+&mmc0 {
+	dmas = <&dma1 0xd1
+		&dma1 0xd2>;
+	dma-names = "tx", "rx";
+};
+
 Example:
 	dmac: dma-mux0 {
 		compatible = "renesas,shdma-mux";
diff --git a/drivers/dma/sh/shdma.h b/drivers/dma/sh/shdma.h
index 8394424..991316f 100644
--- a/drivers/dma/sh/shdma.h
+++ b/drivers/dma/sh/shdma.h
@@ -23,6 +23,7 @@
 #define SH_DMAE_TCR_MAX 0x00FFFFFF	/* 16MB */
 
 struct device;
+struct device_node;
 
 struct sh_dmae_chan {
 	struct shdma_chan shdma_chan;
@@ -33,6 +34,11 @@ struct sh_dmae_chan {
 	int pm_error;
 };
 
+struct sh_dmae_filter_info {
+	u32			hw_req;
+	struct device_node	*of_node;
+};
+
 struct sh_dmae_device {
 	struct shdma_dev shdma_dev;
 	struct sh_dmae_chan *chan[SH_DMAE_MAX_CHANNELS];
@@ -42,6 +48,7 @@ struct sh_dmae_device {
 	void __iomem *dmars;
 	unsigned int chcr_offset;
 	u32 chcr_ie_bit;
+	struct sh_dmae_filter_info filter_info;
 };
 
 struct sh_dmae_regs {
diff --git a/drivers/dma/sh/shdmac.c b/drivers/dma/sh/shdmac.c
index 9ee3c28..fcaed8d 100644
--- a/drivers/dma/sh/shdmac.c
+++ b/drivers/dma/sh/shdmac.c
@@ -22,6 +22,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/of_dma.h>
 #include <linux/slab.h>
 #include <linux/interrupt.h>
 #include <linux/dmaengine.h>
@@ -665,6 +666,63 @@ static const struct shdma_ops sh_dmae_shdma_ops = {
 	.get_partial = sh_dmae_get_partial,
 };
 
+static bool sh_dmae_chan_filter(struct dma_chan *chan, void *arg)
+{
+	struct sh_dmae_filter_info *info = arg;
+	struct shdma_chan *schan = to_shdma_chan(chan);
+	int match = info->hw_req;
+
+	if (match < 0)
+		/* No slave requested - arbitrary channel */
+		return true;
+
+	dev_dbg(schan->dev, "%s(): trying %s for 0x%x\n", __func__,
+		info->of_node->full_name, match);
+
+	if (schan->dev->of_node != info->of_node)
+		return false;
+
+	return !sh_dmae_set_slave(schan, match, true);
+}
+
+static struct dma_chan *sh_dmae_of_xlate(struct of_phandle_args *dma_spec,
+					 struct of_dma *ofdma)
+{
+	struct sh_dmae_filter_info *info = ofdma->of_dma_data;
+	u32 id = dma_spec->args[0];
+	dma_cap_mask_t mask;
+	struct dma_chan *chan;
+
+	if (dma_spec->args_count != 1)
+		return NULL;
+
+	dma_cap_zero(mask);
+	/* Only slave DMA channels can be allocated via DT */
+	dma_cap_set(DMA_SLAVE, mask);
+
+	info->hw_req = id;
+	info->of_node = dma_spec->np;
+
+	chan = dma_request_channel(mask, sh_dmae_chan_filter, info);
+	if (chan)
+		to_shdma_chan(chan)->hw_req = id;
+
+	return chan;
+}
+
+static int sh_dmae_of_add(struct device *dev, struct sh_dmae_device *shdev)
+{
+	u32 cells;
+	int ret = of_property_read_u32(dev->of_node, "#dma-cells", &cells);
+
+	dev_dbg(dev, "%s(): %u (%d)\n", __func__, cells, ret);
+	if (ret < 0 || !cells)
+		return 0;
+
+	return of_dma_controller_register(dev->of_node,
+					  sh_dmae_of_xlate, &shdev->filter_info);
+}
+
 static const struct of_device_id sh_dmae_of_match[] = {
 	{.compatible = "renesas,shdma-r8a73a4", .data = r8a73a4_shdma_devid,},
 	{.compatible = "renesas,shdma-r8a7740", .data = r8a7740_shdma_devid,},
@@ -845,6 +903,10 @@ static int sh_dmae_probe(struct platform_device *pdev)
 		} while (irq_cnt < pdata->channel_num && chanirq_res);
 	}
 
+	err = sh_dmae_of_add(&pdev->dev, shdev);
+	if (err < 0)
+		goto of_add_err;
+
 	/* Create DMA Channel */
 	for (i = 0; i < irq_cnt; i++) {
 		err = sh_dmae_chan_probe(shdev, i, chan_irq[i], chan_flag[i]);
@@ -869,6 +931,8 @@ edmadevreg:
 	pm_runtime_get(&pdev->dev);
 
 chan_probe_err:
+	of_dma_controller_free(pdev->dev.of_node);
+of_add_err:
 	sh_dmae_chan_remove(shdev);
 
 #if defined(CONFIG_CPU_SH4) || defined(CONFIG_ARCH_SHMOBILE)
@@ -895,6 +959,8 @@ static int sh_dmae_remove(struct platform_device *pdev)
 	struct sh_dmae_device *shdev = platform_get_drvdata(pdev);
 	struct dma_device *dma_dev = &shdev->shdma_dev.dma_dev;
 
+	of_dma_controller_free(pdev->dev.of_node);
+
 	dma_async_device_unregister(dma_dev);
 
 	spin_lock_irq(&sh_dmae_lock);
-- 
1.7.2.5

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