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ASoC: rockchip: i2s: fix playback after runtime resume

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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: f0447f6cbb ("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
This commit is contained in:
John Keeping 2018-01-08 16:01:04 +00:00 committed by Mark Brown
parent 4fbd8d194f
commit c66234cfed
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GPG Key ID: 24D68B725D5487D0
1 changed files with 6 additions and 0 deletions
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6
sound/soc/rockchip/rockchip_i2s.c
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@ -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;
}