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 --- v2 changes: - Fix rockchip_i2s_precious_reg to return true for I2S_RXDR
sound/soc/rockchip/rockchip_i2s.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/sound/soc/rockchip/rockchip_i2s.c b/sound/soc/rockchip/rockchip_i2s.c index 908211e1d6fc..eb27f6c24bf7 100644 --- a/sound/soc/rockchip/rockchip_i2s.c +++ b/sound/soc/rockchip/rockchip_i2s.c @@ -504,6 +504,7 @@ static bool rockchip_i2s_rd_reg(struct device *dev, unsigned int reg) 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(struct device *dev, unsigned int reg) 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(struct device *dev, unsigned int reg) static bool rockchip_i2s_precious_reg(struct device *dev, unsigned int reg) { switch (reg) { + case I2S_RXDR: + return true; default: return false; }