* [PATCH 1/3] ASoC: soc-dai: add shared BCLK clock for cross-DAI rate constraints
2026-04-30 7:46 [PATCH 0/3] ASoC: add shared BCLK rate constraint for cross-DAI coordination Troy Mitchell
@ 2026-04-30 7:46 ` Troy Mitchell
2026-04-30 12:01 ` Mark Brown
2026-04-30 7:46 ` [PATCH 2/3] ASoC: soc-pcm: constrain hw_params when DAIs share the same BCLK Troy Mitchell
2026-04-30 7:46 ` [PATCH 3/3] ASoC: spacemit: declare shared BCLK for cross-DAI rate constraint Troy Mitchell
2 siblings, 1 reply; 6+ messages in thread
From: Troy Mitchell @ 2026-04-30 7:46 UTC (permalink / raw)
To: Liam Girdwood, Mark Brown, Jaroslav Kysela, Takashi Iwai,
Yixun Lan
Cc: linux-sound, linux-kernel, linux-riscv, spacemit, jinmei.wei,
Troy Mitchell
Add a bclk field to struct snd_soc_dai and a helper function
snd_soc_dai_set_bclk_clk() that platform drivers can use to declare
which clock is their BCLK.
Also cache the bclk_ratio in snd_soc_dai_set_bclk_ratio() so that
the framework can use it later in hw_rule evaluation for TDM
configurations where BCLK = rate * slots * slot_width.
When multiple DAIs on the same card share the same physical BCLK
(detected via clk_is_match()), the ASoC core can automatically
constrain their hw_params so that the resulting BCLK rates are
compatible. This commit adds the data structure support; the actual
constraint logic follows in the next patch.
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
include/sound/soc-dai.h | 7 +++++++
sound/soc/soc-dai.c | 17 +++++++++++++++++
2 files changed, 24 insertions(+)
diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
index 6a42812bba8c..df010a91b350 100644
--- a/include/sound/soc-dai.h
+++ b/include/sound/soc-dai.h
@@ -17,6 +17,7 @@
struct snd_pcm_substream;
struct snd_soc_dapm_widget;
struct snd_compr_stream;
+struct clk;
/*
* DAI hardware audio formats.
@@ -188,6 +189,8 @@ int snd_soc_dai_set_pll(struct snd_soc_dai *dai,
int snd_soc_dai_set_bclk_ratio(struct snd_soc_dai *dai, unsigned int ratio);
+void snd_soc_dai_set_bclk_clk(struct snd_soc_dai *dai, struct clk *bclk);
+
/* Digital Audio interface formatting */
int snd_soc_dai_get_fmt_max_priority(const struct snd_soc_pcm_runtime *rtd);
u64 snd_soc_dai_get_fmt(const struct snd_soc_dai *dai, int priority);
@@ -473,6 +476,10 @@ struct snd_soc_dai {
unsigned int symmetric_channels;
unsigned int symmetric_sample_bits;
+ /* shared BCLK clock for cross-DAI rate constraints */
+ struct clk *bclk;
+ unsigned int bclk_ratio; /* BCLK = rate * bclk_ratio (0 = use channels * sample_bits) */
+
/* parent platform/codec */
struct snd_soc_component *component;
diff --git a/sound/soc/soc-dai.c b/sound/soc/soc-dai.c
index 2f370fda1266..6c5a02562e74 100644
--- a/sound/soc/soc-dai.c
+++ b/sound/soc/soc-dai.c
@@ -116,10 +116,27 @@ int snd_soc_dai_set_bclk_ratio(struct snd_soc_dai *dai, unsigned int ratio)
dai->driver->ops->set_bclk_ratio)
ret = dai->driver->ops->set_bclk_ratio(dai, ratio);
+ dai->bclk_ratio = ratio;
+
return soc_dai_ret(dai, ret);
}
EXPORT_SYMBOL_GPL(snd_soc_dai_set_bclk_ratio);
+/**
+ * snd_soc_dai_set_bclk_clk - set the BCLK clock for shared clock detection
+ * @dai: DAI
+ * @bclk: BCLK clock pointer (or NULL to clear)
+ *
+ * When multiple DAIs share the same physical BCLK (detected via
+ * clk_is_match()), the ASoC core will automatically constrain their
+ * hw_params so that the resulting BCLK rates are compatible.
+ */
+void snd_soc_dai_set_bclk_clk(struct snd_soc_dai *dai, struct clk *bclk)
+{
+ dai->bclk = bclk;
+}
+EXPORT_SYMBOL_GPL(snd_soc_dai_set_bclk_clk);
+
int snd_soc_dai_get_fmt_max_priority(const struct snd_soc_pcm_runtime *rtd)
{
struct snd_soc_dai *dai;
--
2.54.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 2/3] ASoC: soc-pcm: constrain hw_params when DAIs share the same BCLK
2026-04-30 7:46 [PATCH 0/3] ASoC: add shared BCLK rate constraint for cross-DAI coordination Troy Mitchell
2026-04-30 7:46 ` [PATCH 1/3] ASoC: soc-dai: add shared BCLK clock for cross-DAI rate constraints Troy Mitchell
@ 2026-04-30 7:46 ` Troy Mitchell
2026-04-30 12:05 ` Mark Brown
2026-04-30 7:46 ` [PATCH 3/3] ASoC: spacemit: declare shared BCLK for cross-DAI rate constraint Troy Mitchell
2 siblings, 1 reply; 6+ messages in thread
From: Troy Mitchell @ 2026-04-30 7:46 UTC (permalink / raw)
To: Liam Girdwood, Mark Brown, Jaroslav Kysela, Takashi Iwai,
Yixun Lan
Cc: linux-sound, linux-kernel, linux-riscv, spacemit, jinmei.wei,
Troy Mitchell
When multiple CPU DAIs on the same sound card share the same physical
BCLK, add a hw_rule during PCM open that constrains the sample rate so
the resulting BCLK rate stays consistent across all sharing DAIs.
The hw_rule is registered unconditionally for every DAI that has a bclk
clock pointer set. The actual peer scanning happens inside the rule
callback at hw_refine time: it walks all DAIs on the card, looking for
an active peer that shares the same physical BCLK (via clk_is_match())
and has already completed hw_params (checked via dai->symmetric_rate
!= 0). This ensures the constraint uses the real BCLK rate established
by the peer's clk_set_rate() in hw_params, not a stale boot-time
default.
The first DAI to complete hw_params is unconstrained (no active peer
yet); subsequent DAIs are constrained to match.
The rule supports two modes:
- If the DAI has an explicit bclk_ratio set (e.g. for TDM where
BCLK = rate * slots * slot_width), the rate is constrained to
active_bclk_rate / bclk_ratio.
- Otherwise, the default formula BCLK = rate * channels * sample_bits
is used to derive the valid rate range.
The constraint is purely additive: DAIs that do not set a bclk clock
pointer are completely unaffected.
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
sound/soc/soc-pcm.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 113 insertions(+)
diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 9b12eedb77c3..31f48795a653 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -12,6 +12,7 @@
#include <linux/kernel.h>
#include <linux/init.h>
+#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/pinctrl/consumer.h>
#include <linux/slab.h>
@@ -467,6 +468,111 @@ static int soc_pcm_apply_symmetry(struct snd_pcm_substream *substream,
return 0;
}
+/*
+ * Shared BCLK constraint: when multiple DAIs share the same physical BCLK,
+ * constrain hw_params so that the BCLK rate (rate * channels * sample_bits,
+ * or rate * slots * slot_width for TDM) remains consistent.
+ */
+
+static int soc_pcm_shared_bclk_rule_rate(struct snd_pcm_hw_params *params,
+ struct snd_pcm_hw_rule *rule)
+{
+ struct snd_soc_dai *dai = rule->private;
+ struct snd_soc_card *card = dai->component->card;
+ struct snd_soc_pcm_runtime *rtd;
+ struct snd_soc_dai *other_dai;
+ unsigned long active_bclk_rate = 0;
+ struct snd_interval *rate = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
+ struct snd_interval constraint = { .empty = 1 };
+ unsigned int target_rate;
+ int i;
+
+ /* Scan all DAIs on the card for an active peer sharing the same BCLK */
+ for_each_card_rtds(card, rtd) {
+ for_each_rtd_cpu_dais(rtd, i, other_dai) {
+ if (other_dai == dai)
+ continue;
+ if (!other_dai->bclk)
+ continue;
+ if (!snd_soc_dai_active(other_dai))
+ continue;
+ /*
+ * Skip peers whose hw_params hasn't run yet.
+ * symmetric_rate is set by soc_pcm_set_dai_params()
+ * after snd_soc_dai_hw_params(), so non-zero means
+ * the DAI's clk_set_rate() has already executed.
+ */
+ if (!other_dai->symmetric_rate)
+ continue;
+ if (!clk_is_match(dai->bclk, other_dai->bclk))
+ continue;
+
+ active_bclk_rate = clk_get_rate(other_dai->bclk);
+ if (active_bclk_rate)
+ goto found;
+ }
+ }
+
+ return 0;
+
+found:
+ if (dai->bclk_ratio) {
+ /*
+ * Driver has set an explicit BCLK ratio (e.g. for TDM where
+ * BCLK = rate * slots * slot_width). The only valid rate is
+ * active_bclk_rate / bclk_ratio.
+ */
+ target_rate = active_bclk_rate / dai->bclk_ratio;
+
+ constraint.min = target_rate;
+ constraint.max = target_rate;
+ } else {
+ struct snd_interval *channels = hw_param_interval(params,
+ SNDRV_PCM_HW_PARAM_CHANNELS);
+ struct snd_interval *sample_bits = hw_param_interval(params,
+ SNDRV_PCM_HW_PARAM_SAMPLE_BITS);
+
+ /*
+ * Default: BCLK = rate * channels * sample_bits.
+ * Calculate the range of valid rates given the current
+ * channel and sample_bits intervals.
+ */
+ if (!channels->min || !sample_bits->min)
+ return 0;
+
+ constraint.max = active_bclk_rate /
+ ((unsigned long)channels->min * sample_bits->min);
+
+ if (channels->max && sample_bits->max)
+ constraint.min = active_bclk_rate /
+ ((unsigned long)channels->max * sample_bits->max);
+ else
+ constraint.min = constraint.max;
+ }
+
+ constraint.integer = 1;
+ constraint.empty = 0;
+
+ return snd_interval_refine(rate, &constraint);
+}
+
+static int soc_pcm_apply_shared_bclk(struct snd_pcm_substream *substream,
+ struct snd_soc_dai *dai)
+{
+ if (!dai->bclk)
+ return 0;
+
+ dev_dbg(dai->dev,
+ "ASoC: registering shared BCLK rate constraint\n");
+
+ return snd_pcm_hw_rule_add(substream->runtime, 0,
+ SNDRV_PCM_HW_PARAM_RATE,
+ soc_pcm_shared_bclk_rule_rate, dai,
+ SNDRV_PCM_HW_PARAM_CHANNELS,
+ SNDRV_PCM_HW_PARAM_SAMPLE_BITS,
+ -1);
+}
+
static int soc_pcm_params_symmetry(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *params)
{
@@ -903,6 +1009,13 @@ static int __soc_pcm_open(struct snd_soc_pcm_runtime *rtd,
if (ret != 0)
goto err;
}
+
+ /* Shared BCLK constraint across DAIs on the same card */
+ for_each_rtd_cpu_dais(rtd, i, dai) {
+ ret = soc_pcm_apply_shared_bclk(substream, dai);
+ if (ret != 0)
+ goto err;
+ }
dynamic:
snd_soc_runtime_activate(rtd, substream->stream);
ret = 0;
--
2.54.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 3/3] ASoC: spacemit: declare shared BCLK for cross-DAI rate constraint
2026-04-30 7:46 [PATCH 0/3] ASoC: add shared BCLK rate constraint for cross-DAI coordination Troy Mitchell
2026-04-30 7:46 ` [PATCH 1/3] ASoC: soc-dai: add shared BCLK clock for cross-DAI rate constraints Troy Mitchell
2026-04-30 7:46 ` [PATCH 2/3] ASoC: soc-pcm: constrain hw_params when DAIs share the same BCLK Troy Mitchell
@ 2026-04-30 7:46 ` Troy Mitchell
2 siblings, 0 replies; 6+ messages in thread
From: Troy Mitchell @ 2026-04-30 7:46 UTC (permalink / raw)
To: Liam Girdwood, Mark Brown, Jaroslav Kysela, Takashi Iwai,
Yixun Lan
Cc: linux-sound, linux-kernel, linux-riscv, spacemit, jinmei.wei,
Troy Mitchell
On SpacemiT K3, multiple I2S controllers share the same physical BCLK
(c_bclk). Declare this clock via snd_soc_dai_set_bclk_clk() so the
ASoC core can automatically constrain hw_params when one controller is
already streaming.
For K1, c_bclk is NULL (obtained via devm_clk_get_optional_enabled),
so this call is a no-op and behavior is unchanged.
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
sound/soc/spacemit/k1_i2s.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/sound/soc/spacemit/k1_i2s.c b/sound/soc/spacemit/k1_i2s.c
index 4e655d714623..989e82b3c5b4 100644
--- a/sound/soc/spacemit/k1_i2s.c
+++ b/sound/soc/spacemit/k1_i2s.c
@@ -306,6 +306,8 @@ static int spacemit_i2s_dai_probe(struct snd_soc_dai *dai)
spacemit_i2s_init(i2s);
+ snd_soc_dai_set_bclk_clk(dai, i2s->c_bclk);
+
return 0;
}
--
2.54.0
^ permalink raw reply related [flat|nested] 6+ messages in thread