Patch "ASoC: rockchip: i2s: fix playback after runtime resume" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

ASoC: rockchip: i2s: fix playback after runtime resume

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
asoc-rockchip-i2s-fix-playback-after-runtime-resume.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: John Keeping <[email protected]>
Date: Mon, 8 Jan 2018 16:01:04 +0000
Subject: ASoC: rockchip: i2s: fix playback after runtime resume

From: John Keeping <[email protected]>

commit c66234cfedfc3e6e3b62563a5f2c1562be09a35d upstream.

When restoring registers during runtime resume, we must not write to I2S_TXDR which is the transmit FIFO as this queues up a sample to be output and pushes all of the output channels down by one.

This can be demonstrated with the speaker-test utility:

for i in a b c; do speaker-test -c 2 -s 1; done

which should play a test through the left speaker three times but if the I2S hardware starts runtime suspended the first sample will be played through the right speaker.

Fix this by marking I2S_TXDR as volatile (which also requires marking it as readble, even though it technically isn't). This seems to be the most robust fix, the alternative of giving I2S_TXDR a default value is more fragile since it does not prevent regcache writing to the register in all circumstances.

While here, also fix the configuration of I2S_RXDR and I2S_FIFOLR; these are not writable so they do not suffer from the same problem as I2S_TXDR but reading from I2S_RXDR does suffer from a similar problem.

---
 sound/soc/rockchip/rockchip_i2s.c |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -504,6 +504,7 @@ static bool rockchip_i2s_rd_reg(struct d
 	case I2S_INTCR:
 	case I2S_XFER:
 	case I2S_CLR:
+	case I2S_TXDR:
 	case I2S_RXDR:
 	case I2S_FIFOLR:
 	case I2S_INTSR:

@@ -518,6 +519,9 @@ static bool rockchip_i2s_volatile_reg(st
 	switch (reg) {
 	case I2S_INTSR:
 	case I2S_CLR:
+	case I2S_FIFOLR:
+	case I2S_TXDR:
+	case I2S_RXDR:
 		return true;
 	default:
 		return false;

@@ -527,6 +531,8 @@ static bool rockchip_i2s_volatile_reg(st
 static bool rockchip_i2s_precious_reg(struct device *dev, unsigned int reg)
 {
 	switch (reg) {
+	case I2S_RXDR:
+		return true;
 	default:
 		return false;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/asoc-rockchip-i2s-fix-playback-after-runtime-resume.patch