[PATCH AUTOSEL 6.17] ASoC: renesas: msiof: add .symmetric_xxx on snd_soc_dai_driver

[Sasha Levin <sashal@kernel.org>]

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

[ Upstream commit ab77fa5533e4d1dcfdd2711b9b1e166e4ed57dab ]

MSIOF TX/RX are sharing same clock. Adds .symmetric_xxx flags.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Link: https://patch.msgid.link/87a52jyuu6.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 programs both TX and RX registers in one shot while a stream
  starts (`sound/soc/renesas/rcar/msiof.c:168`-
  `sound/soc/renesas/rcar/msiof.c:259`), and the in-file [NOTE-BOTH-
  SETTING] warns that touching those registers while the peer direction
  is active triggers hardware FSERRs. Without symmetry constraints, the
  second stream can request a different rate/width and the ALSA core
  will try to reconfigure the shared clock, recreating the FSERR
  condition that the driver is trying to avoid.
- Setting `.symmetric_rate`, `.symmetric_channels`, and
  `.symmetric_sample_bits` to `1` in the DAI driver (`sound/soc/renesas/
  rcar/msiof.c:395`-`sound/soc/renesas/rcar/msiof.c:398`) tells the core
  to force the late-starting stream to inherit the parameters already in
  use, preventing those invalid reconfigurations and the resulting
  DMA/FSERR failures that users encounter when running full-duplex with
  mismatched parameters.
- The fix is tiny, self-contained, and matches the documented hardware
  constraint; it only restricts configurations that never worked in
  practice because TX/RX share clocks and register programming, so
  regression risk is minimal.
- The fields being set have existed in the stable series since well
  before MSIOF support landed, so the patch applies cleanly without
  dependencies, and it comes with Tested-by coverage from Renesas
  hardware. Stable users with duplex workloads benefit directly from the
  enforced symmetry.

 sound/soc/renesas/rcar/msiof.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sound/soc/renesas/rcar/msiof.c b/sound/soc/renesas/rcar/msiof.c
index 36d31ab8ac6a5..7a9ecc73231a8 100644
--- a/sound/soc/renesas/rcar/msiof.c
+++ b/sound/soc/renesas/rcar/msiof.c
@@ -292,6 +292,9 @@ static struct snd_soc_dai_driver msiof_dai_driver = {
 		.channels_max	= 2,
 	},
 	.ops = &msiof_dai_ops,
+	.symmetric_rate		= 1,
+	.symmetric_channels	= 1,
+	.symmetric_sample_bits	= 1,
 };
 
 static struct snd_pcm_hardware msiof_pcm_hardware = {
-- 
2.51.0