Message-Id: <20200117153056.31363-1-geert+renesas@glider.be>
Date:   Fri, 17 Jan 2020 16:30:56 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     dmaengine@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves

Currently it is not easy to find out which DMA channels are in use, and
which slave devices are using which channels.

Fix this by creating two symlinks between the DMA channel and the actual
slave device when a channel is requested:
  1. A "slave" symlink from DMA channel to slave device,
  2. A "dma:<name>" symlink slave device to DMA channel.
When the channel is released, the symlinks are removed again.
The latter requires keeping track of the slave device and the channel
name in the dma_chan structure.

Note that this is limited to channel request functions for requesting an
exclusive slave channel that take a device pointer (dma_request_chan()
and dma_request_slave_channel*()).

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
v2:
  - Add DMA_SLAVE_NAME macro,
  - Also handle channels from FIXME,
  - Add backlinks from slave device to DMA channel,

On r8a7791/koelsch, the following new symlinks are created:

    /sys/devices/platform/soc/
    ├── e6700000.dma-controller/dma/dma0chan0/slave -> ../../../e6e20000.spi
    ├── e6700000.dma-controller/dma/dma0chan1/slave -> ../../../e6e20000.spi
    ├── e6700000.dma-controller/dma/dma0chan2/slave -> ../../../ee100000.sd
    ├── e6700000.dma-controller/dma/dma0chan3/slave -> ../../../ee100000.sd
    ├── e6700000.dma-controller/dma/dma0chan4/slave -> ../../../ee160000.sd
    ├── e6700000.dma-controller/dma/dma0chan5/slave -> ../../../ee160000.sd
    ├── e6700000.dma-controller/dma/dma0chan6/slave -> ../../../e6e68000.serial
    ├── e6700000.dma-controller/dma/dma0chan7/slave -> ../../../e6e68000.serial
    ├── e6720000.dma-controller/dma/dma1chan0/slave -> ../../../e6b10000.spi
    ├── e6720000.dma-controller/dma/dma1chan1/slave -> ../../../e6b10000.spi
    ├── e6720000.dma-controller/dma/dma1chan2/slave -> ../../../ee140000.sd
    ├── e6720000.dma-controller/dma/dma1chan3/slave -> ../../../ee140000.sd
    ├── e6b10000.spi/dma:rx -> ../e6720000.dma-controller/dma/dma1chan1
    ├── e6b10000.spi/dma:tx -> ../e6720000.dma-controller/dma/dma1chan0
    ├── e6e20000.spi/dma:rx -> ../e6700000.dma-controller/dma/dma0chan1
    ├── e6e20000.spi/dma:tx -> ../e6700000.dma-controller/dma/dma0chan0
    ├── e6e68000.serial/dma:rx -> ../e6700000.dma-controller/dma/dma0chan7
    ├── e6e68000.serial/dma:tx -> ../e6700000.dma-controller/dma/dma0chan6
    ├── ee100000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan3
    ├── ee100000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan2
    ├── ee140000.sd/dma:rx -> ../e6720000.dma-controller/dma/dma1chan3
    ├── ee140000.sd/dma:tx -> ../e6720000.dma-controller/dma/dma1chan2
    ├── ee160000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan5
    └── ee160000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan4

On r8a77951/salvator-xs:

    /sys/devices/platform/soc/
    ├── e6460000.dma-controller/dma/dma4chan0/slave -> ../../../e659c000.usb
    ├── e6460000.dma-controller/dma/dma4chan1/slave -> ../../../e659c000.usb
    ├── e6470000.dma-controller/dma/dma5chan0/slave -> ../../../e659c000.usb
    ├── e6470000.dma-controller/dma/dma5chan1/slave -> ../../../e659c000.usb
    ├── e6510000.i2c/dma:tx -> ../e7300000.dma-controller/dma/dma7chan0
    ├── e6550000.serial/dma:rx -> ../e7310000.dma-controller/dma/dma8chan1
    ├── e6550000.serial/dma:tx -> ../e7310000.dma-controller/dma/dma8chan0
    ├── e6590000.usb/dma:ch0 -> ../e65a0000.dma-controller/dma/dma2chan0
    ├── e6590000.usb/dma:ch1 -> ../e65a0000.dma-controller/dma/dma2chan1
    ├── e6590000.usb/dma:ch2 -> ../e65b0000.dma-controller/dma/dma3chan0
    ├── e6590000.usb/dma:ch3 -> ../e65b0000.dma-controller/dma/dma3chan1
    ├── e659c000.usb/dma:ch0 -> ../e6460000.dma-controller/dma/dma4chan0
    ├── e659c000.usb/dma:ch1 -> ../e6460000.dma-controller/dma/dma4chan1
    ├── e659c000.usb/dma:ch2 -> ../e6470000.dma-controller/dma/dma5chan0
    ├── e659c000.usb/dma:ch3 -> ../e6470000.dma-controller/dma/dma5chan1
    ├── e65a0000.dma-controller/dma/dma2chan0/slave -> ../../../e6590000.usb
    ├── e65a0000.dma-controller/dma/dma2chan1/slave -> ../../../e6590000.usb
    ├── e65b0000.dma-controller/dma/dma3chan0/slave -> ../../../e6590000.usb
    ├── e65b0000.dma-controller/dma/dma3chan1/slave -> ../../../e6590000.usb
    ├── e7300000.dma-controller/dma/dma7chan0/slave -> ../../../e6510000.i2c
    ├── e7310000.dma-controller/dma/dma8chan0/slave -> ../../../e6550000.serial
    └── e7310000.dma-controller/dma/dma8chan1/slave -> ../../../e6550000.serial
---
 drivers/dma/dmaengine.c   | 37 +++++++++++++++++++++++++++++++------
 include/linux/dmaengine.h |  4 ++++
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 56a8420c388679d3..617c84cf6800962b 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -60,6 +60,8 @@ static long dmaengine_ref_count;
 
 /* --- sysfs implementation --- */
 
+#define DMA_SLAVE_NAME	"slave"
+
 /**
  * dev_to_dma_chan - convert a device pointer to its sysfs container object
  * @dev - device node
@@ -730,11 +732,11 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
 	if (has_acpi_companion(dev) && !chan)
 		chan = acpi_dma_request_slave_chan_by_name(dev, name);
 
-	if (chan) {
-		/* Valid channel found or requester needs to be deferred */
-		if (!IS_ERR(chan) || PTR_ERR(chan) == -EPROBE_DEFER)
-			return chan;
-	}
+	if (PTR_ERR(chan) == -EPROBE_DEFER)
+		return chan;
+
+	if (!IS_ERR_OR_NULL(chan))
+		goto found;
 
 	/* Try to find the channel via the DMA filter map(s) */
 	mutex_lock(&dma_list_mutex);
@@ -754,7 +756,23 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
 	}
 	mutex_unlock(&dma_list_mutex);
 
-	return chan ? chan : ERR_PTR(-EPROBE_DEFER);
+	if (!IS_ERR_OR_NULL(chan))
+		goto found;
+
+	return ERR_PTR(-EPROBE_DEFER);
+
+found:
+	chan->slave = dev;
+	chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
+	if (!chan->name)
+		return ERR_PTR(-ENOMEM);
+
+	if (sysfs_create_link(&chan->dev->device.kobj, &dev->kobj,
+			      DMA_SLAVE_NAME))
+		dev_err(dev, "Cannot create DMA %s symlink\n", DMA_SLAVE_NAME);
+	if (sysfs_create_link(&dev->kobj, &chan->dev->device.kobj, chan->name))
+		dev_err(dev, "Cannot create DMA %s symlink\n", chan->name);
+	return chan;
 }
 EXPORT_SYMBOL_GPL(dma_request_chan);
 
@@ -812,6 +830,13 @@ void dma_release_channel(struct dma_chan *chan)
 	/* drop PRIVATE cap enabled by __dma_request_channel() */
 	if (--chan->device->privatecnt == 0)
 		dma_cap_clear(DMA_PRIVATE, chan->device->cap_mask);
+	if (chan->slave) {
+		sysfs_remove_link(&chan->slave->kobj, chan->name);
+		kfree(chan->name);
+		chan->name = NULL;
+		chan->slave = NULL;
+	}
+	sysfs_remove_link(&chan->dev->device.kobj, DMA_SLAVE_NAME);
 	mutex_unlock(&dma_list_mutex);
 }
 EXPORT_SYMBOL_GPL(dma_release_channel);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 2cd1d6d7ef0fcce5..2804da93e27e114b 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -238,10 +238,12 @@ struct dma_router {
 /**
  * struct dma_chan - devices supply DMA channels, clients use them
  * @device: ptr to the dma device who supplies this channel, always !%NULL
+ * @slave: ptr to the device using this channel
  * @cookie: last cookie value returned to client
  * @completed_cookie: last completed cookie for this channel
  * @chan_id: channel ID for sysfs
  * @dev: class device for sysfs
+ * @name: backlink name for sysfs
  * @device_node: used to add this to the device chan list
  * @local: per-cpu pointer to a struct dma_chan_percpu
  * @client_count: how many clients are using this channel
@@ -252,12 +254,14 @@ struct dma_router {
  */
 struct dma_chan {
 	struct dma_device *device;
+	struct device *slave;
 	dma_cookie_t cookie;
 	dma_cookie_t completed_cookie;
 
 	/* sysfs */
 	int chan_id;
 	struct dma_chan_dev *dev;
+	const char *name;
 
 	struct list_head device_node;
 	struct dma_chan_percpu __percpu *local;
-- 
2.17.1

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