[media] tw686x: audio: Allow to configure the period size

Currently, the driver has a fixed period size of 4096 bytes
(2048 frames). Since this hardware can configure the audio
capture size, this commit allows a period size range of [512-4096].

This is very useful to reduce the audio latency.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/pci/tw686x/tw686x.h

@@ -27,7 +27,6 @@
 #define TYPE_SECOND_GEN		0x10
 #define TW686X_DEF_PHASE_REF	0x1518
 
-#define TW686X_AUDIO_PAGE_SZ		4096
 #define TW686X_AUDIO_PAGE_MAX		16
 #define TW686X_AUDIO_PERIODS_MIN	2
 #define TW686X_AUDIO_PERIODS_MAX	TW686X_AUDIO_PAGE_MAX
@@ -139,7 +138,9 @@ struct tw686x_dev {
 	struct tw686x_video_channel *video_channels;
 	struct tw686x_audio_channel *audio_channels;
 
-	int audio_rate; /* per-device value */
+	/* Per-device audio parameters */
+	int audio_rate;
+	int period_size;
 
 	struct timer_list dma_delay_timer;
 	u32 pending_dma_en; /* must be protected by lock */