[PATCH] dmaengine: device must have at least one channel

[Viresh Kumar <viresh.kumar@linaro.org>]

The DMA device can't be registered if it doesn't have any channels
registered at all. Moreover, it leads to memory leak and is reported by
kmemleak as (on 3.10 kernel, and same shall happen on mainline):

unreferenced object 0xffffffc09e597240 (size 64):
  comm "swapper/0", pid 1, jiffies 4294877736 (age 7060.280s)
  hex dump (first 32 bytes):
    00 00 00 00 c0 ff ff ff 30 00 00 ff 00 00 00 ff  ........0.......
    00 00 00 ff 00 00 00 ff 00 00 00 ff 00 00 00 ff  ................
  backtrace:
    [<ffffffc0003079ec>] create_object+0x148/0x2a0
    [<ffffffc000cc150c>] kmemleak_alloc+0x80/0xbc
    [<ffffffc000303a7c>] kmem_cache_alloc_trace+0x120/0x1ac
    [<ffffffc00054771c>] dma_async_device_register+0x160/0x46c
    [<ffffffc000548958>] foo_probe+0x1a0/0x264
    [<ffffffc0005d6658>] platform_drv_probe+0x14/0x20
    [<ffffffc0005d50cc>] driver_probe_device+0x160/0x374
    [<ffffffc0005d538c>] __driver_attach+0x60/0x90
    [<ffffffc0005d3e78>] bus_for_each_dev+0x7c/0xb0
    [<ffffffc0005d4a0c>] driver_attach+0x1c/0x28
    [<ffffffc0005d459c>] bus_add_driver+0x124/0x248
    [<ffffffc0005d59cc>] driver_register+0x90/0x110
    [<ffffffc0005d6bf4>] platform_driver_register+0x58/0x64
    [<ffffffc00142a70c>] foo_driver_init+0x10/0x1c
    [<ffffffc000200878>] do_one_initcall+0xac/0x148
    [<ffffffc00140096c>] kernel_init_freeable+0x1a0/0x258

Return -ENODEV from dma_async_device_register() on such a case.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
Hi Vinod,

Sorry if the fundamentals behind this patch are completely incorrect,
i.e. We *can't* register a dma device with 0 channels. Its been long
that I have worked on dma stuff :)

 drivers/dma/dmaengine.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 8c9f45fd55fc..6b535262ac5d 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -997,6 +997,13 @@ int dma_async_device_register(struct dma_device *device)
 		}
 		chan->client_count = 0;
 	}
+
+	if (!chancnt) {
+		dev_err(device->dev, "%s: device has no channels!\n", __func__);
+		rc = -ENODEV;
+		goto err_out;
+	}
+
 	device->chancnt = chancnt;
 
 	mutex_lock(&dma_list_mutex);
-- 
2.7.4