linux-kernel - [PATCH v2 4/7] ASoC: soc-dai: define possible idle TDM slot modes

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Message-Id: <20251221-tdm-idle-slots-v2-4-ed4d96413aec@gmail.com>
Date: Sun, 21 Dec 2025 19:36:00 +1000
From: James Calligeros <jcalligeros99@...il.com>
To: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, 
 Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>, 
 Shengjiu Wang <shengjiu.wang@....com>, Jaroslav Kysela <perex@...ex.cz>, 
 Takashi Iwai <tiwai@...e.com>, Shenghao Ding <shenghao-ding@...com>, 
 Kevin Lu <kevin-lu@...com>, Baojun Xu <baojun.xu@...com>
Cc: linux-sound@...r.kernel.org, devicetree@...r.kernel.org, 
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, asahi@...ts.linux.dev, 
 James Calligeros <jcalligeros99@...il.com>
Subject: [PATCH v2 4/7] ASoC: soc-dai: define possible idle TDM slot modes

Some audio devices, such as certain Texas Instruments codecs,
include configurable bus keepers. We currently don't have
a standardised way to configure such hardware, and instead
rely on the hardware initialising setting itself up into a
sane state. There are situations where this is insufficient,
however, and some platforms require more concrete guarantees
as to the state of the bus, and being able to explicitly
configure bus keepers enables this.

For example, some Apple Silicon machines have an odd bus topology where
the SDOUT pins of all codecs are split across two data lines, which
are summed via an OR gate in front of the receiving port on the
SoC's I2S peripheral. Each line must transmit 0 while a codec
on the other line is actively transmitting data, or the SoC
will receive garbage data. To do this, one codec on each line
must be configured to transmit zeroes during the other line's
active TDM slots.

Thus, we define seven possible bus-keeping modes that a device can
be in: NONE (UB/as initialised), OFF (explicitly disabled), ZERO
(actively transmit a 0), PULLDOWN, HIZ (floating), PULLUP, and
DRIVE_HIGH.

These will be consumed by CODEC/CPU drivers via a common DAI
op, enabling the explicit configuration of bus keepers where
required.

Signed-off-by: James Calligeros <jcalligeros99@...il.com>
---
 include/sound/soc-dai.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
index 224396927aef..44dd06add52e 100644
--- a/include/sound/soc-dai.h
+++ b/include/sound/soc-dai.h
@@ -52,6 +52,21 @@ struct snd_compr_stream;
 #define SND_SOC_POSSIBLE_DAIFMT_AC97		(1 << SND_SOC_DAI_FORMAT_AC97)
 #define SND_SOC_POSSIBLE_DAIFMT_PDM		(1 << SND_SOC_DAI_FORMAT_PDM)

+/*
+ * DAI TDM slot idle modes
+ *
+ * Describes a CODEC/CPU's behaviour when not actively receiving or
+ * transmitting on a given TDM slot. NONE is undefined behaviour.
+ * Add new modes to the end.
+ */
+#define SND_SOC_DAI_TDM_IDLE_NONE	0
+#define SND_SOC_DAI_TDM_IDLE_OFF	1
+#define SND_SOC_DAI_TDM_IDLE_ZERO	2
+#define SND_SOC_DAI_TDM_IDLE_PULLDOWN	3
+#define SND_SOC_DAI_TDM_IDLE_HIZ	4
+#define SND_SOC_DAI_TDM_IDLE_PULLUP	5
+#define SND_SOC_DAI_TDM_IDLE_DRIVE_HIGH	6
+
 /*
  * DAI Clock gating.
  *

-- 
2.52.0