[ALSA] aoa i2sbus: Stop Apple i2s DMA gracefully

This fixes the problem of getting extra bytes inserted at the
beginning of a recording when using the Apple i2s interface and DBDMA
controller.  It turns out that we can't just abort the DMA; we have to
let it stop at the end of a command, and then wait for the S7 bit to
be set before turning off the DBDMA controller.  Doing that for
playback doesn't seem to be necessary, but doesn't hurt either.
We use the technique used by the Darwin driver: make each transfer
command branch to a stop command if the S0 status bit is set.  Thus we
can ask the DMA controller to stop at the end of the current command
by setting S0.
The interrupt routine now looks at and clears the status word of the
DBDMA command ring.  This is necessary so it can know when the DBDMA
controller has seen that S0 is set, and so when it should look for the
DBDMA controller being stopped and S7 being set.  This also ended up
simplifying the calculation in i2sbus_pcm_pointer.
Tested on a 15 inch albook.
[Addition by Johannes]
I modified this patch and added the suspend/resume bits to it to get my
powermac into a decent state when playing sound across suspend to disk
that has a different bitrate from what the firmware programs the
hardware to.
I also added the SNDRV_PCM_INFO_JOINT_DUPLEX flag because it seemed the
right thing to do and I was looking at the info stuff.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/aoa/soundbus/i2sbus/i2sbus-core.c

@@ -41,8 +41,8 @@ static int alloc_dbdma_descriptor_ring(struct i2sbus_dev *i2sdev,
 				       struct dbdma_command_mem *r,
 				       int numcmds)
 {
-	/* one more for rounding */
-	r->size = (numcmds+1) * sizeof(struct dbdma_cmd);
+	/* one more for rounding, one for branch back, one for stop command */
+	r->size = (numcmds + 3) * sizeof(struct dbdma_cmd);
 	/* We use the PCI APIs for now until the generic one gets fixed
 	 * enough or until we get some macio-specific versions
 	 */
@@ -377,11 +377,8 @@ static int i2sbus_suspend(struct macio_dev* dev, pm_message_t state)
 		if (i2sdev->sound.pcm) {
 			/* Suspend PCM streams */
 			snd_pcm_suspend_all(i2sdev->sound.pcm);
-			/* Probably useless as we handle
-			 * power transitions ourselves */
-			snd_power_change_state(i2sdev->sound.pcm->card,
-					       SNDRV_CTL_POWER_D3hot);
 		}
+
 		/* Notify codecs */
 		list_for_each_entry(cii, &i2sdev->sound.codec_list, list) {
 			err = 0;
@@ -390,7 +387,11 @@ static int i2sbus_suspend(struct macio_dev* dev, pm_message_t state)
 			if (err)
 				ret = err;
 		}
+
+		/* wait until streams are stopped */
+		i2sbus_wait_for_stop_both(i2sdev);
 	}
+
 	return ret;
 }
 
@@ -402,6 +403,9 @@ static int i2sbus_resume(struct macio_dev* dev)
 	int err, ret = 0;
 
 	list_for_each_entry(i2sdev, &control->list, item) {
+		/* reset i2s bus format etc. */
+		i2sbus_pcm_prepare_both(i2sdev);
+
 		/* Notify codecs so they can re-initialize */
 		list_for_each_entry(cii, &i2sdev->sound.codec_list, list) {
 			err = 0;
@@ -410,12 +414,6 @@ static int i2sbus_resume(struct macio_dev* dev)
 			if (err)
 				ret = err;
 		}
-		/* Notify Alsa */
-		if (i2sdev->sound.pcm) {
-			/* Same comment as above, probably useless */
-			snd_power_change_state(i2sdev->sound.pcm->card,
-					       SNDRV_CTL_POWER_D0);
-		}
 	}
 
 	return ret;

sound/aoa/soundbus/i2sbus/i2sbus.h

@@ -10,6 +10,7 @@
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/mutex.h>
+#include <linux/completion.h>
 
 #include <sound/pcm.h>
 
@@ -34,6 +35,7 @@ struct dbdma_command_mem {
 	void *space;
 	int size;
 	u32 running:1;
+	u32 stopping:1;
 };
 
 struct pcm_info {
@@ -45,6 +47,7 @@ struct pcm_info {
 	u32 frame_count;
 	struct dbdma_command_mem dbdma_ring;
 	volatile struct dbdma_regs __iomem *dbdma;
+	struct completion *stop_completion;
 };
 
 enum {
@@ -101,6 +104,9 @@ i2sbus_tx_intr(int irq, void *devid);
 extern irqreturn_t
 i2sbus_rx_intr(int irq, void *devid);
 
+extern void i2sbus_wait_for_stop_both(struct i2sbus_dev *i2sdev);
+extern void i2sbus_pcm_prepare_both(struct i2sbus_dev *i2sdev);
+
 /* control specific functions */
 extern int i2sbus_control_init(struct macio_dev* dev,
 			       struct i2sbus_control **c);