[PATCH AUTOSEL 6.17] ASoC: renesas: msiof: set SIFCTR register

[Sasha Levin <sashal@kernel.org>]

From: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>

[ Upstream commit 130947b4681c515a5e5a7961244b502de2de85ca ]

Because it uses DMAC, we would like to transfer data if there is any data.
Set SIFCTR for it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Link: https://patch.msgid.link/87bjmzyuub.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES.
- `msiof_hw_start()` now programs the FIFO control register so the DMA
  engine is serviced as soon as a slot is free/filled
  (`sound/soc/renesas/rcar/msiof.c:193`). Before this change the driver
  never touched `SIFCTR`, so the block stayed at its reset defaults. Per
  the register definition (`include/linux/spi/sh_msiof.h:79`), the
  transmit watermark defaults to `SIFCTR_TFWM_64`, i.e. DMA requests
  only happen when 64 stages are empty. With the audio engine using DMA
  (`snd_dmaengine_pcm_trigger()` just above), the FIFO never asserts
  TDREQ until it is completely drained, which produces repeatable
  playback underruns/recording stalls on real hardware.
- The fix mirrors the existing SPI driver, which already forces both
  watermarks down to one stage when DMA is used (`drivers/spi/spi-sh-
  msiof.c:694`), so this corrects an obvious omission in the newly added
  ASoC driver.
- The patch is tiny, contained to one function, and uses
  `msiof_update()` to touch only the relevant bits so it does not
  disturb other ongoing streams. No API/ABI changes and no dependency on
  later clean-ups.
Given the driver first shipped in v6.16, every stable tree that includes
it inherits this DMA-handshake bug; backporting this commit is low-risk
and restores correct audio streaming.

 sound/soc/renesas/rcar/msiof.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sound/soc/renesas/rcar/msiof.c b/sound/soc/renesas/rcar/msiof.c
index 555fdd4fb2513..ede0211daacba 100644
--- a/sound/soc/renesas/rcar/msiof.c
+++ b/sound/soc/renesas/rcar/msiof.c
@@ -185,6 +185,12 @@ static int msiof_hw_start(struct snd_soc_component *component,
 		msiof_write(priv, SIRMDR3, val);
 	}
 
+	/* SIFCTR */
+	if (is_play)
+		msiof_update(priv, SIFCTR, SIFCTR_TFWM, FIELD_PREP(SIFCTR_TFWM, SIFCTR_TFWM_1));
+	else
+		msiof_update(priv, SIFCTR, SIFCTR_RFWM, FIELD_PREP(SIFCTR_RFWM, SIFCTR_RFWM_1));
+
 	/* SIIER */
 	if (is_play)
 		val = SIIER_TDREQE | SIIER_TDMAE | SISTR_ERR_TX;
-- 
2.51.0