FAILED: patch "[PATCH] ASoC: qcom: q6apm-dai: wrap the position of a full ring to 0" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 0ea3e0b196f9dcc17b40ac881a6efef06459975b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107051147-failed-6.18-0ea3e0b196f9@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 0ea3e0b196f9dcc17b40ac881a6efef06459975b Mon Sep 17 00:00:00 2001
From: Vladyslav Tymoshchuk <tvlad744@gmail.com>
Date: Wed, 14 Oct 2026 19:27:00 +0300
Subject: [PATCH] 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>
---
 sound/soc/qcom/qdsp6/q6apm-dai.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/sound/soc/qcom/qdsp6/q6apm-dai.c b/sound/soc/qcom/qdsp6/q6apm-dai.c
index b0b10ba51c99d..58beaf906b9ff 100644
--- a/sound/soc/qcom/qdsp6/q6apm-dai.c
+++ b/sound/soc/qcom/qdsp6/q6apm-dai.c
@@ -613,11 +613,15 @@ static snd_pcm_uframes_t q6apm_dai_pointer(struct snd_soc_component *component,
 		ptr = bytes_to_frames(runtime, index);
 		return ptr;
 	}
-	ptr = q6apm_get_hw_pointer(prtd->graph, substream->stream) * runtime->period_size;
-	if (ptr)
-		return ptr - 1;
+	/*
+	 * The hw pointer counts the period buffers the DSP has returned in
+	 * this lap, 1..periods. A full lap is the start of the ring again:
+	 * report 0 rather than one frame less, so that the position of a
+	 * drained buffer reaches appl_ptr and ALSA sees the underrun.
+	 */
+	ptr = q6apm_get_hw_pointer(prtd->graph, substream->stream) % runtime->periods;
 
-	return 0;
+	return ptr * runtime->period_size;
 }
 
 static int q6apm_dai_hw_params(struct snd_soc_component *component,
-- 
2.53.0