[PATCH v9 12/14] ALSA: pcm: add an optional reset operation under the stream lock

[Joonho Lee <mynameisjune111@gmail.com>]

A driver may need to synchronize private capture accounting with the
common RESET pointer observation and the core's position rebase.

Add an optional reset operation called under the member's stream lock.
Expose snd_pcm_lib_reset() so the callback can retain common pointer and
time handling. On zero return the core completes that member's rebase
before unlocking it. Drivers without the callback retain the ioctl path.
The operation is also used after a successful prepare.

Zero permits the position rebase; it does not promise XRUN recovery.
A negative return skips the core rebase, so a callback returning an error
must leave coherent pointer state even after partial work.

Linked RESET and prepare stop at the first error without rollback.
Earlier callback members may already have completed. Legacy members keep
the existing post_action policy. Applications must recover the group
after partial failure before relying on shared positions.

This adds an internal kernel operation and no userspace ioctl or layout.
Out-of-tree modules using snd_pcm_ops need to be rebuilt.

Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>

---
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -77,6 +77,26 @@
 			     unsigned long offset);
 	int (*mmap)(struct snd_pcm_substream *substream, struct vm_area_struct *vma);
 	int (*ack)(struct snd_pcm_substream *substream);
+	/*
+	 * Optional RESET operation, also used after a successful prepare.
+	 * Called with this substream's PCM lock held; atomic streams must not
+	 * sleep. Do not reacquire the PCM lock through snd_pcm_lib_ioctl().
+	 * snd_pcm_lib_reset() provides the common pointer update under this
+	 * lock. The core completes the position and appl_ptr rebase before
+	 * unlocking a successful member.
+	 *
+	 * Return zero to let the core complete the position rebase. As with
+	 * the legacy RESET ioctl, zero does not guarantee recovery from XRUN;
+	 * callers must still handle the stream state and subsequent I/O errors.
+	 * On a negative return the core does not finish the rebase, so the
+	 * callback must leave coherent pointer state even after partial work.
+	 *
+	 * Linked RESET/prepare
+	 * stops at the first error without rollback. Earlier callback members
+	 * retain their completed reset; legacy members retain the existing
+	 * post_action policy. An error does not guarantee unchanged state.
+	 */
+	int (*reset)(struct snd_pcm_substream *substream);
 };
 
 /*
@@ -1179,6 +1199,7 @@
 {
 	substream->runtime->std_sync_id = true;
 }
+int snd_pcm_lib_reset(struct snd_pcm_substream *substream);
 int snd_pcm_lib_ioctl(struct snd_pcm_substream *substream,
 		      unsigned int cmd, void *arg);                      
 void snd_pcm_period_elapsed_under_stream_lock(struct snd_pcm_substream *substream);
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1760,20 +1760,39 @@
 }
 EXPORT_SYMBOL(snd_pcm_hw_params_bits);
 
-static int snd_pcm_lib_ioctl_reset(struct snd_pcm_substream *substream,
-				   void *arg)
+/**
+ * snd_pcm_lib_reset - Reset the pointer while holding the PCM stream lock
+ * @substream: PCM substream
+ *
+ * Context: PCM stream lock held. The caller must not hold driver locks
+ * acquired by the pointer or XRUN callbacks.
+ *
+ * Update a running stream through the ordinary pointer path. Other states
+ * start at zero. Pointer errors keep the existing RESET return semantics;
+ * a zero return does not imply recovery from XRUN.
+ * This helper does not update appl_ptr or acquire the stream lock.
+ *
+ * Return: zero.
+ */
+int snd_pcm_lib_reset(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 
-	guard(pcm_stream_lock_irqsave)(substream);
-	if (snd_pcm_running(substream) &&
-	    snd_pcm_update_hw_ptr(substream) >= 0)
+	if (snd_pcm_running(substream) && snd_pcm_update_hw_ptr(substream) >= 0)
 		runtime->status->hw_ptr %= runtime->buffer_size;
 	else {
 		runtime->status->hw_ptr = 0;
 		runtime->hw_ptr_wrap = 0;
 	}
 	return 0;
+}
+EXPORT_SYMBOL(snd_pcm_lib_reset);
+
+static int snd_pcm_lib_ioctl_reset(struct snd_pcm_substream *substream,
+				   void *arg)
+{
+	guard(pcm_stream_lock_irqsave)(substream);
+	return snd_pcm_lib_reset(substream);
 }
 
 static int snd_pcm_lib_ioctl_channel_info(struct snd_pcm_substream *substream,
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1988,7 +1988,31 @@
 			    snd_pcm_state_t state)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
-	int err = snd_pcm_ops_ioctl(substream, SNDRV_PCM_IOCTL1_RESET, NULL);
+	int err;
+
+	if (substream->ops->reset) {
+		/*
+		 * Complete this member before releasing its PCM lock. A later
+		 * linked member may fail; RESET has no group rollback operation.
+		 */
+		guard(pcm_stream_lock_irq)(substream);
+
+		err = substream->ops->reset(substream);
+		if (err < 0)
+			return err;
+		runtime->hw_ptr_base = 0;
+		runtime->hw_ptr_interrupt = runtime->status->hw_ptr -
+			runtime->status->hw_ptr % runtime->period_size;
+		runtime->silence_start = runtime->status->hw_ptr;
+		runtime->silence_filled = 0;
+		runtime->control->appl_ptr = runtime->status->hw_ptr;
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+		    runtime->silence_size > 0)
+			snd_pcm_playback_silence(substream, ULONG_MAX);
+		return 0;
+	}
+
+	err = snd_pcm_ops_ioctl(substream, SNDRV_PCM_IOCTL1_RESET, NULL);
 	if (err < 0)
 		return err;
 	guard(pcm_stream_lock_irq)(substream);
@@ -2004,6 +2028,9 @@
 			       snd_pcm_state_t state)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	if (substream->ops->reset)
+		return;
 	guard(pcm_stream_lock_irq)(substream);
 	runtime->control->appl_ptr = runtime->status->hw_ptr;
 	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&