ASoC: qcom: q6apm-dai: wrap the position of a full ring to 0

q6apm_dai_pointer() turns the number of period buffers the DSP has
returned in the current lap, 1..periods, into a position and reports
one frame less than that. Commit a93dad6f4e6a ("ASoC: q6apm-dai: make
use of q6apm_get_hw_pointer") added the "- 1" so that the end of the
ring is not reported as a position equal to the buffer size.

One frame short has a cost once the application stops feeding the
stream. The DSP returns the last queued buffer and the position stops
at appl_ptr - 1, so avail stays at buffer_size - 1, below the default
stop_threshold. The DSP sends nothing more as its queue is empty, so
no period interrupt comes either: ALSA never detects the underrun and
the stream stays RUNNING. A poll-driven application that missed its
last wakeup waits forever, and drain only ends on its timeout, with
-EIO. On capture, the last frame of each period is held back until
the next one.

Before that commit the position wrapped to 0 at the end of the ring.
Do that again. A full lap is the start of the ring, and
snd_pcm_update_hw_ptr0() accounts for the wrap: the position cannot
move by more than one lap between two updates, as each returned buffer
calls snd_pcm_period_elapsed() and the DSP holds at most periods
buffers.

Seen on a OnePlus Pad 3 (SM8750) with PipeWire in interrupt-driven
scheduling: after a stall the PCM sat at hw_ptr 78239, appl_ptr 78240
(avail 3839 of 3840) for two hours.

Fixes: a93dad6f4e6a ("ASoC: q6apm-dai: make use of q6apm_get_hw_pointer")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Vladyslav Tymoshchuk <tvlad744@gmail.com>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Tested-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Link: https://patch.msgid.link/20261014162703.10172-2-tvlad744@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

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