dmaengine: add interface of dma_get_slave_channel

Hello Zhangfei Gao,

The patch 7bb587f4eef8: "dmaengine: add interface of dma_get_slave_channel" from Jun 28, 2013, leads to the following
warning: "drivers/dma/dmaengine.c:531 dma_get_slave_channel()
error: potential NULL dereference 'chan'."

drivers/dma/dmaengine.c
516 struct dma_chan *dma_get_slave_channel(struct dma_chan *chan) 517 {
518 int err = -EBUSY;
519
520 /* lock against __dma_request_channel */
521 mutex_lock(&dma_list_mutex);
522
523 if (chan->client_count = 0)
524 err = dma_chan_get(chan);
525 else

   526                  chan = NULL;
                        ^^^^^^^^^^^
   527  
   528          mutex_unlock(&dma_list_mutex);
   529  
   530          if (err)
   531                  pr_debug("%s: failed to get %s: (%d)\n",
   532                          __func__, dma_chan_name(chan), err);
                                                        ^^^^

Dereferenced here.

533
534 return chan;

regards,
dan carpenter

Thanks Dan for point out.

I am sorry, make does not report such error here, is it config related.

Dear Vinod

Could I update this patch and resend to you?
Change to:
struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)

{
         int err = -EBUSY;

         /* lock against __dma_request_channel */
         mutex_lock(&dma_list_mutex);

         if (chan->client_count = 0) {
                 err = dma_chan_get(chan);
                 if (err)
                         pr_debug("%s: failed to get %s: (%d)\n",
                                 __func__, dma_chan_name(chan), err);
         } else
                 chan = NULL;

         mutex_unlock(&dma_list_mutex);

         return chan;
}

Sorry for inconvenience.

Thanks