[ALSA] s3c24xx-pcm: fix hw_params dma handling

Since the PCM emulation can call multiple times to hw_setup(), but we
can only once allocate/request the DMA channel, we have to handle
this gracefully.
Signed-off-by: Harald Welte <laforge@openmoko.org>
Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/soc/s3c24xx/s3c24xx-pcm.c

@@ -158,6 +158,9 @@ static int s3c24xx_pcm_hw_params(struct snd_pcm_substream *substream,
 	if (!dma)
 		return 0;
 
+	/* this may get called several times by oss emulation
+	 * with different params -HW */
+	if (prtd->params == NULL) {
 		/* prepare DMA */
 		prtd->params = dma;
 
@@ -171,6 +174,7 @@ static int s3c24xx_pcm_hw_params(struct snd_pcm_substream *substream,
 			DBG(KERN_ERR "failed to get dma channel\n");
 			return ret;
 		}
+	}
 
 	/* channel needs configuring for mem=>device, increment memory addr,
 	 * sync to pclk, half-word transfers to the IIS-FIFO. */