staging: bcm2835-audio: Use coherent device buffers

The memory access to the pages allocated with
SNDRV_DMA_TYPE_CONTINUOUS are basically non-coherent, and it becomes a
problem when a process accesses via mmap.

For the more consistent access, use the device coherent memory, just
by replacing the call pattern in the allocator helpers.

The only point we need to be careful for is the device object passed
there; since bcm2835-audio driver creates fake devices and each card
is created on top of that, we need to pass its parent device as the
real device object.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c

@@ -345,8 +345,8 @@ int snd_bcm2835_new_pcm(struct bcm2835_chip *chip, u32 numchannels)
 
 	/* pre-allocation of buffers */
 	/* NOTE: this may fail */
-	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
-					      snd_dma_continuous_data(GFP_KERNEL),
+	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+					      chip->card->dev->parent,
 					      snd_bcm2835_playback_hw.buffer_bytes_max,
 					      snd_bcm2835_playback_hw.buffer_bytes_max);
 
@@ -371,8 +371,8 @@ int snd_bcm2835_new_spdif_pcm(struct bcm2835_chip *chip)
 
 	/* pre-allocation of buffers */
 	/* NOTE: this may fail */
-	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
-		snd_dma_continuous_data(GFP_KERNEL),
+	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+		chip->card->dev->parent,
 		snd_bcm2835_playback_spdif_hw.buffer_bytes_max, snd_bcm2835_playback_spdif_hw.buffer_bytes_max);
 
 	return 0;
@@ -404,8 +404,8 @@ int snd_bcm2835_new_simple_pcm(struct bcm2835_chip *chip,
 
 	snd_pcm_lib_preallocate_pages_for_all(
 		pcm,
-		SNDRV_DMA_TYPE_CONTINUOUS,
-		snd_dma_continuous_data(GFP_KERNEL),
+		SNDRV_DMA_TYPE_DEV,
+		chip->card->dev->parent,
 		snd_bcm2835_playback_hw.buffer_bytes_max,
 		snd_bcm2835_playback_hw.buffer_bytes_max);