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3bd860dcf9Troy Mitchell <troy.mitchell@linux.spacemit.com> says:
On some SoCs (e.g. SpacemiT K3), multiple I2S controllers share the
same physical BCLK. When one controller is already streaming, the
others must use hw_params that result in the same BCLK rate, otherwise
the shared clock would be reconfigured and corrupt the active stream.
This series adds framework-level support for this constraint:
Patch 1 adds the dt-bindings for the spacemit,k3-i2s compatible.
The K3 SoC uses the same I2S IP as K1 but requires additional clocks:
a dedicated sysclk_div, along with c_sysclk and c_bclk which are
shared across multiple I2S controllers.
Patch 2 adds a DEFINE_GUARD wrapping snd_soc_card_mutex_lock() and
snd_soc_card_mutex_unlock() so that scope-based locking picks up the
SND_SOC_CARD_CLASS_RUNTIME lockdep subclass.
Patch 3 adds the constraint logic in soc-pcm.c. During PCM open,
every DAI that has a bclk clock pointer gets a hw_rule registered
unconditionally. The rule callback runs at hw_refine time: it scans
the card for an active peer sharing the same physical BCLK (via
clk_is_match()) that has already completed hw_params, then constrains
the current stream's rate to match the established BCLK rate. The
first DAI to complete hw_params is unconstrained; subsequent DAIs
must match. Two modes are supported:
- Default (I2S): BCLK = rate * channels * sample_bits. The rule
derives the valid rate range from the current channel and
sample_bits intervals.
- Explicit ratio (TDM): if the driver sets dai->bclk_ratio
(e.g. slots * slot_width), the rule computes the single valid
rate as active_bclk_rate / bclk_ratio.
This series was prompted by review feedback on the SpacemiT K3 I2S
series, where a vendor-specific fixed-sample-rate property was rejected
in favor of a generic framework solution:
https://lore.kernel.org/all/afFqgF6ZRwYdfUmL@sirena.co.uk/
Link: https://patch.msgid.link/20260522-i2s-same-blk-v4-0-a71a86faaa20@linux.spacemit.com
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