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bcm2835-i2s: fail capture open cleanly when FIFO clear has no clock #7586

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Merged
pelwell merged 1 commit into from
Sep 1, 2026
+27 −6
Merged

bcm2835-i2s: fail capture open cleanly when FIFO clear has no clock #7586

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33 changes: 27 additions & 6 deletions sound/soc/bcm/bcm2835-i2s.c
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Original file line number Diff line number Diff line change
Expand Up @@ -149,8 +149,8 @@ static void bcm2835_i2s_stop_clock(struct bcm2835_i2s_dev *dev)
dev->clk_prepared = false;
}

static void bcm2835_i2s_clear_fifos(struct bcm2835_i2s_dev *dev,
bool tx, bool rx)
static int bcm2835_i2s_clear_fifos(struct bcm2835_i2s_dev *dev,
bool tx, bool rx)
{
int timeout = 1000;
uint32_t syncval;
Expand Down Expand Up @@ -187,8 +187,9 @@ static void bcm2835_i2s_clear_fifos(struct bcm2835_i2s_dev *dev,
/* Wait for 2 PCM clock cycles */

/*
* Toggle the SYNC flag. After 2 PCM clock cycles it can be read back
* FIXME: This does not seem to work for slave mode!
* Toggle the SYNC flag. After 2 PCM clock cycles it can be read back.
* The reset will timeout in clock consumer mode without an external
* clock.
*/
regmap_read(dev->i2s_regmap, BCM2835_I2S_CS_A_REG, &syncval);
syncval &= BCM2835_I2S_SYNC;
Expand All @@ -204,7 +205,8 @@ static void bcm2835_i2s_clear_fifos(struct bcm2835_i2s_dev *dev,
}

if (!timeout)
dev_err(dev->dev, "I2S SYNC error!\n");
dev_err(dev->dev,
"FIFO clear timed out: no PCM clock (clock consumer with the provider not running?)\n");

/* Stop clock if it was not running before */
if (!clk_was_prepared)
Expand All @@ -213,6 +215,14 @@ static void bcm2835_i2s_clear_fifos(struct bcm2835_i2s_dev *dev,
/* Restore I2S state */
regmap_update_bits(dev->i2s_regmap, BCM2835_I2S_CS_A_REG,
BCM2835_I2S_RXON | BCM2835_I2S_TXON, i2s_active_state);

/*
* Without the SYNC round trip the FIFOs were not actually cleared:
* starting DMA on top of a stale FIFO makes RX free-run (DREQ stuck
* high, the same dead word re-read at bus speed) and the state then
* survives further stream cycles. Fail the stream instead.
*/
return timeout ? 0 : -EIO;
}

static int bcm2835_i2s_set_dai_fmt(struct snd_soc_dai *dai,
Expand Down Expand Up @@ -588,6 +598,11 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
| BCM2835_I2S_RX(0x20), 0xffffffff);

/* Clear FIFOs */
/*
* May time out benignly here: on clock-consumer links the provider's
* clocks are often not running yet at hw_params time; the clear that
* must succeed is the one in .prepare.
*/
bcm2835_i2s_clear_fifos(dev, true, true);

dev_dbg(dev->dev,
Expand Down Expand Up @@ -636,7 +651,13 @@ static int bcm2835_i2s_prepare(struct snd_pcm_substream *substream,
bcm2835_i2s_clear_fifos(dev, true, false);
else if (substream->stream == SNDRV_PCM_STREAM_CAPTURE
&& (cs_reg & BCM2835_I2S_RXD))
bcm2835_i2s_clear_fifos(dev, false, true);
/*
* Stale RX data with no working clock cannot be cleared: DMA
* would free-run over the dead FIFO (DREQ stuck high) and the
* poisoned state survives stream cycles. Fail this capture
* open instead of recording garbage.
*/
return bcm2835_i2s_clear_fifos(dev, false, true);

return 0;
}
Expand Down
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