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@glider.be>
Tested-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Link: https://lore.kernel.org/r/20200117153056.31363-1-geert+renesas@glider.be
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 51a2f2b1b2dea45c6c462f419ee3b623b3491885..f3ef4edd4de178dea5e920cb8df4d467d937b800 100644 (file)
--- 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 f52f274773edc5edbf6e4e041152a08b987babd4..fef69a9c5824e3395be49a2110f9961367053810 100644 (file)
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -294,10 +294,12 @@ 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
@@ -308,12 +310,14 @@ 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;