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From c66234cfedfc3e6e3b62563a5f2c1562be09a35d Mon Sep 17 00:00:00 2001
From: John Keeping <john@metanate.com>
Date: Mon, 8 Jan 2018 16:01:04 +0000
Subject: [PATCH] ASoC: rockchip: i2s: fix playback after runtime resume
Git-commit: c66234cfedfc3e6e3b62563a5f2c1562be09a35d
Patch-mainline: v4.16-rc1
References: bsc#1051510

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.

Fixes: f0447f6cbb20 ("ASoC: rockchip: i2s: restore register during runtime_suspend/resume cycle", 2016-09-07)
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
Acked-by: Takashi Iwai <tiwai@suse.de>

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

--- a/sound/soc/rockchip/rockchip_i2s.c
+++ b/sound/soc/rockchip/rockchip_i2s.c
@@ -476,6 +476,7 @@ 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:
@@ -490,6 +491,9 @@ 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;
@@ -499,6 +503,8 @@ 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;
 	}