This patch adds the ALSA PCM device infrastructure. It creates a new
PCM device with one playback and one capture stream.

The hardware capabilities (formats, rates, channels) are defined in
`tascam_pcm_hw`. The core PCM operations (`snd_pcm_ops`) for both
playback and capture are implemented, including open, close, hw_params,
prepare, and pointer callbacks.

The trigger callback is a stub for now. This commit allows user-space
applications to interact with the ALSA device, but no audio will be
streamed yet.

Signed-off-by: Šerif Rami <ramiserifpersia@gmail.com>
---
 sound/usb/usx2y/us144mkii.c          |  20 ++++-
 sound/usb/usx2y/us144mkii.h          |  46 +++++++++++-
 sound/usb/usx2y/us144mkii_capture.c  | 108 +++++++++++++++++++++++++++
 sound/usb/usx2y/us144mkii_pcm.c      |  77 +++++++++++++++++++
 sound/usb/usx2y/us144mkii_pcm.h      |  76 +++++++++++++++++++
 sound/usb/usx2y/us144mkii_playback.c | 108 +++++++++++++++++++++++++++
 6 files changed, 429 insertions(+), 6 deletions(-)
 create mode 100644 sound/usb/usx2y/us144mkii_capture.c
 create mode 100644 sound/usb/usx2y/us144mkii_pcm.c
 create mode 100644 sound/usb/usx2y/us144mkii_pcm.h
 create mode 100644 sound/usb/usx2y/us144mkii_playback.c

diff --git a/sound/usb/usx2y/us144mkii.c b/sound/usb/usx2y/us144mkii.c
index f438f222baec..9b14390efb56 100644
--- a/sound/usb/usx2y/us144mkii.c
+++ b/sound/usb/usx2y/us144mkii.c
@@ -22,7 +22,7 @@ MODULE_LICENSE("GPL");
  *            Defaults to "US144MKII".
  * @param enable: Array of booleans to enable or disable each device.
  *                Defaults to {1, 0, ..., 0} (first device enabled).
- * @param dev_idx: Internal counter for probed TASCAM devices.
+ * @param dev_idx: Internal counter for the number of TASCAM devices probed.
  */
 static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
 static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
@@ -36,7 +36,7 @@ static int tascam_suspend(struct usb_interface *intf, pm_message_t message);
 static int tascam_resume(struct usb_interface *intf);
 
 /**
- * tascam_card_private_free() - Frees private data for the sound card.
+ * tascam_card_private_free() - Frees private data associated with the sound
  * card.
  * @card: Pointer to the ALSA sound card instance.
  *
@@ -58,12 +58,12 @@ static void tascam_card_private_free(struct snd_card *card)
  * @intf: The USB interface being probed.
  * @usb_id: The USB device ID.
  *
- * This function is the entry point for the USB driver on device match.
+ * This function is the entry point for the USB driver when a matching device
  * is found. It performs initial device setup, including:
  * - Checking for the second interface (MIDI) and associating it.
  * - Performing a vendor-specific handshake with the device.
  * - Setting alternate settings for USB interfaces.
- * - Creating and registering the ALSA sound card.
+ * - Creating and registering the ALSA sound card and PCM device.
  *
  * Return: 0 on success, or a negative error code on failure.
  */
@@ -152,6 +152,18 @@ static int tascam_probe(struct usb_interface *intf,
 	tascam->card = card;
 	tascam->iface0 = intf;
 
+	spin_lock_init(&tascam->lock);
+
+	err = snd_pcm_new(card, "US144MKII PCM", 0, 1, 1, &tascam->pcm);
+	if (err < 0)
+		goto free_card;
+	tascam->pcm->private_data = tascam;
+	strscpy(tascam->pcm->name, "US144MKII PCM", sizeof(tascam->pcm->name));
+
+	err = tascam_init_pcm(tascam->pcm);
+	if (err < 0)
+		goto free_card;
+
 	strscpy(card->driver, DRIVER_NAME, sizeof(card->driver));
 	if (dev->descriptor.idProduct == USB_PID_TASCAM_US144) {
 		strscpy(card->shortname, "TASCAM US-144",
diff --git a/sound/usb/usx2y/us144mkii.h b/sound/usb/usx2y/us144mkii.h
index 9f59863fab57..44f3b44bbf3b 100644
--- a/sound/usb/usx2y/us144mkii.h
+++ b/sound/usb/usx2y/us144mkii.h
@@ -21,18 +21,60 @@
 #define MODE_VAL_HANDSHAKE_READ 0x0000
 #define USB_CTRL_TIMEOUT_MS 1000
 
+/* --- Audio Format Configuration --- */
+#define BYTES_PER_SAMPLE 3
+#define NUM_CHANNELS 4
+#define BYTES_PER_FRAME (NUM_CHANNELS * BYTES_PER_SAMPLE)
+
+/* --- USB Control Message Protocol --- */
+#define RT_D2H_VENDOR_DEV (USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE)
+#define VENDOR_REQ_MODE_CONTROL 0x49
+#define MODE_VAL_HANDSHAKE_READ 0x0000
+#define USB_CTRL_TIMEOUT_MS 1000
+
+struct tascam_card;
+
+#include "us144mkii_pcm.h"
+
 /**
- * struct tascam_card - Driver data structure for TASCAM US-144MKII.
+ * struct tascam_card - Main driver data structure for the TASCAM US-144MKII.
  * @dev: Pointer to the USB device.
  * @iface0: Pointer to USB interface 0 (audio).
  * @iface1: Pointer to USB interface 1 (MIDI).
  * @card: Pointer to the ALSA sound card instance.
+ * @pcm: Pointer to the ALSA PCM device.
+ * @playback_substream: Pointer to the active playback PCM substream.
+ * @capture_substream: Pointer to the active capture PCM substream.
+ * @playback_active: Atomic flag indicating if playback is active.
+ * @capture_active: Atomic flag indicating if capture is active.
+ * @driver_playback_pos: Current position in the ALSA playback buffer (frames).
+ * @driver_capture_pos: Current position in the ALSA capture buffer (frames).
+ * @playback_frames_consumed: Total frames consumed by playback.
+ * @capture_frames_processed: Total frames processed for capture.
+ * @current_rate: Currently configured sample rate of the device.
+ * @lock: Main spinlock for protecting shared driver state.
  */
 struct tascam_card {
 	struct usb_device *dev;
 	struct usb_interface *iface0;
 	struct usb_interface *iface1;
 	struct snd_card *card;
+	struct snd_pcm *pcm;
+
+	struct snd_pcm_substream *playback_substream;
+	struct snd_pcm_substream *capture_substream;
+
+	atomic_t playback_active;
+	atomic_t capture_active;
+
+	snd_pcm_uframes_t driver_playback_pos;
+	snd_pcm_uframes_t driver_capture_pos;
+
+	u64 playback_frames_consumed;
+	u64 capture_frames_processed;
+
+	int current_rate;
+	spinlock_t lock;
 };
 
- #endif /* __US144MKII_H */
+#endif /* __US144MKII_H */
diff --git a/sound/usb/usx2y/us144mkii_capture.c b/sound/usb/usx2y/us144mkii_capture.c
new file mode 100644
index 000000000000..f2ce90743d22
--- /dev/null
+++ b/sound/usb/usx2y/us144mkii_capture.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2025 Šerif Rami <ramiserifpersia@gmail.com>
+
+#include "us144mkii.h"
+
+/**
+ * tascam_capture_open() - Opens the PCM capture substream.
+ * @substream: The ALSA PCM substream to open.
+ *
+ * This function sets the hardware parameters for the capture substream
+ * and stores a reference to the substream in the driver's private data.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_capture_open(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	substream->runtime->hw = tascam_pcm_hw;
+	tascam->capture_substream = substream;
+	atomic_set(&tascam->capture_active, 0);
+
+	return 0;
+}
+
+/**
+ * tascam_capture_close() - Closes the PCM capture substream.
+ * @substream: The ALSA PCM substream to close.
+ *
+ * This function clears the reference to the capture substream in the
+ * driver's private data.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_capture_close(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	tascam->capture_substream = NULL;
+
+	return 0;
+}
+
+/**
+ * tascam_capture_prepare() - Prepares the PCM capture substream for use.
+ * @substream: The ALSA PCM substream to prepare.
+ *
+ * This function initializes capture-related counters.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_capture_prepare(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	tascam->driver_capture_pos = 0;
+	tascam->capture_frames_processed = 0;
+
+	return 0;
+}
+
+/**
+ * tascam_capture_pointer() - Returns the current capture pointer position.
+ * @substream: The ALSA PCM substream.
+ *
+ * This function returns the current position of the capture pointer within
+ * the ALSA ring buffer, in frames.
+ *
+ * Return: The current capture pointer position in frames.
+ */
+static snd_pcm_uframes_t
+tascam_capture_pointer(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	u64 pos;
+
+	if (!atomic_read(&tascam->capture_active))
+		return 0;
+
+	guard(spinlock_irqsave)(&tascam->lock);
+	pos = tascam->capture_frames_processed;
+
+	if (runtime->buffer_size == 0)
+		return 0;
+
+	u64 remainder = do_div(pos, runtime->buffer_size);
+
+	return runtime ? remainder : 0;
+}
+
+/**
+ * tascam_capture_ops - ALSA PCM operations for capture.
+ *
+ * This structure defines the callback functions for capture stream operations,
+ * including open, close, ioctl, hardware parameters, hardware free, prepare,
+ * trigger, and pointer.
+ */
+const struct snd_pcm_ops tascam_capture_ops = {
+	.open = tascam_capture_open,
+	.close = tascam_capture_close,
+	.ioctl = snd_pcm_lib_ioctl,
+	.hw_params = tascam_pcm_hw_params,
+	.hw_free = tascam_pcm_hw_free,
+	.prepare = tascam_capture_prepare,
+	.trigger = tascam_pcm_trigger,
+	.pointer = tascam_capture_pointer,
+};
diff --git a/sound/usb/usx2y/us144mkii_pcm.c b/sound/usb/usx2y/us144mkii_pcm.c
new file mode 100644
index 000000000000..be6f0fa4750b
--- /dev/null
+++ b/sound/usb/usx2y/us144mkii_pcm.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2025 Šerif Rami <ramiserifpersia@gmail.com>
+
+#include "us144mkii.h"
+
+const struct snd_pcm_hardware tascam_pcm_hw = {
+	.info = (SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_INTERLEAVED |
+		 SNDRV_PCM_INFO_BLOCK_TRANSFER | SNDRV_PCM_INFO_MMAP_VALID |
+		 SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME),
+	.formats = SNDRV_PCM_FMTBIT_S24_3LE,
+	.rates = (SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_48000 |
+		  SNDRV_PCM_RATE_88200 | SNDRV_PCM_RATE_96000),
+	.rate_min = 44100,
+	.rate_max = 96000,
+	.channels_min = NUM_CHANNELS,
+	.channels_max = NUM_CHANNELS,
+	.buffer_bytes_max = 1024 * 1024,
+	.period_bytes_min = 48 * BYTES_PER_FRAME,
+	.period_bytes_max = 1024 * BYTES_PER_FRAME,
+	.periods_min = 2,
+	.periods_max = 1024,
+};
+
+int tascam_pcm_hw_params(struct snd_pcm_substream *substream,
+			 struct snd_pcm_hw_params *params)
+{
+	return 0;
+}
+
+int tascam_pcm_hw_free(struct snd_pcm_substream *substream)
+{
+	return 0;
+}
+
+int tascam_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+	int err = 0;
+
+	guard(spinlock_irqsave)(&tascam->lock);
+	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_START:
+	case SNDRV_PCM_TRIGGER_RESUME:
+		if (!atomic_read(&tascam->playback_active)) {
+			atomic_set(&tascam->playback_active, 1);
+			atomic_set(&tascam->capture_active, 1);
+		}
+		break;
+	case SNDRV_PCM_TRIGGER_STOP:
+	case SNDRV_PCM_TRIGGER_SUSPEND:
+	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+		if (atomic_read(&tascam->playback_active)) {
+			atomic_set(&tascam->playback_active, 0);
+			atomic_set(&tascam->capture_active, 0);
+		}
+		break;
+	default:
+		err = -EINVAL;
+		break;
+	}
+
+	return err;
+}
+
+int tascam_init_pcm(struct snd_pcm *pcm)
+{
+	struct tascam_card *tascam = pcm->private_data;
+
+	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &tascam_playback_ops);
+	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &tascam_capture_ops);
+
+	snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
+				       tascam->dev->dev.parent, 64 * 1024,
+				       tascam_pcm_hw.buffer_bytes_max);
+
+	return 0;
+}
diff --git a/sound/usb/usx2y/us144mkii_pcm.h b/sound/usb/usx2y/us144mkii_pcm.h
new file mode 100644
index 000000000000..bb8b51f9b6fb
--- /dev/null
+++ b/sound/usb/usx2y/us144mkii_pcm.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+// Copyright (c) 2025 Šerif Rami <ramiserifpersia@gmail.com>
+
+#ifndef __US144MKII_PCM_H
+#define __US144MKII_PCM_H
+
+#include "us144mkii.h"
+
+/**
+ * tascam_pcm_hw - Hardware capabilities for TASCAM US-144MKII PCM.
+ *
+ * Defines the supported PCM formats, rates, channels, and buffer/period sizes
+ * for the TASCAM US-144MKII audio interface.
+ */
+extern const struct snd_pcm_hardware tascam_pcm_hw;
+
+/**
+ * tascam_playback_ops - ALSA PCM operations for playback.
+ *
+ * This structure defines the callback functions for playback stream operations.
+ */
+extern const struct snd_pcm_ops tascam_playback_ops;
+
+/**
+ * tascam_capture_ops - ALSA PCM operations for capture.
+ *
+ * This structure defines the callback functions for capture stream operations.
+ */
+extern const struct snd_pcm_ops tascam_capture_ops;
+
+/**
+ * tascam_init_pcm() - Initializes the ALSA PCM device.
+ * @pcm: Pointer to the ALSA PCM device to initialize.
+ *
+ * This function sets up the PCM operations and preallocates pages for the
+ * PCM buffer.
+ *
+ * Return: 0 on success, or a negative error code on failure.
+ */
+int tascam_init_pcm(struct snd_pcm *pcm);
+
+/**
+ * tascam_pcm_hw_params() - Configures hardware parameters for PCM streams.
+ * @substream: The ALSA PCM substream.
+ * @params: The hardware parameters to apply.
+ *
+ * This function is a stub for handling hardware parameter configuration.
+ *
+ * Return: 0 on success.
+ */
+int tascam_pcm_hw_params(struct snd_pcm_substream *substream,
+			 struct snd_pcm_hw_params *params);
+
+/**
+ * tascam_pcm_hw_free() - Frees hardware parameters for PCM streams.
+ * @substream: The ALSA PCM substream.
+ *
+ * This function is a stub for freeing hardware-related resources.
+ *
+ * Return: 0 on success.
+ */
+int tascam_pcm_hw_free(struct snd_pcm_substream *substream);
+
+/**
+ * tascam_pcm_trigger() - Triggers the start or stop of PCM streams.
+ * @substream: The ALSA PCM substream.
+ * @cmd: The trigger command (e.g., SNDRV_PCM_TRIGGER_START).
+ *
+ * This function handles starting and stopping of playback and capture streams
+ * by setting atomic flags.
+ *
+ * Return: 0 on success, or a negative error code on failure.
+ */
+int tascam_pcm_trigger(struct snd_pcm_substream *substream, int cmd);
+
+#endif /* __US144MKII_PCM_H */
diff --git a/sound/usb/usx2y/us144mkii_playback.c b/sound/usb/usx2y/us144mkii_playback.c
new file mode 100644
index 000000000000..ac582a534123
--- /dev/null
+++ b/sound/usb/usx2y/us144mkii_playback.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2025 Šerif Rami <ramiserifpersia@gmail.com>
+
+#include "us144mkii.h"
+
+/**
+ * tascam_playback_open() - Opens the PCM playback substream.
+ * @substream: The ALSA PCM substream to open.
+ *
+ * This function sets the hardware parameters for the playback substream
+ * and stores a reference to the substream in the driver's private data.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_playback_open(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	substream->runtime->hw = tascam_pcm_hw;
+	tascam->playback_substream = substream;
+	atomic_set(&tascam->playback_active, 0);
+
+	return 0;
+}
+
+/**
+ * tascam_playback_close() - Closes the PCM playback substream.
+ * @substream: The ALSA PCM substream to close.
+ *
+ * This function clears the reference to the playback substream in the
+ * driver's private data.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_playback_close(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	tascam->playback_substream = NULL;
+
+	return 0;
+}
+
+/**
+ * tascam_playback_prepare() - Prepares the PCM playback substream for use.
+ * @substream: The ALSA PCM substream to prepare.
+ *
+ * This function initializes playback-related counters.
+ *
+ * Return: 0 on success.
+ */
+static int tascam_playback_prepare(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+
+	tascam->driver_playback_pos = 0;
+	tascam->playback_frames_consumed = 0;
+
+	return 0;
+}
+
+/**
+ * tascam_playback_pointer() - Returns the current playback pointer position.
+ * @substream: The ALSA PCM substream.
+ *
+ * This function returns the current position of the playback pointer within
+ * the ALSA ring buffer, in frames.
+ *
+ * Return: The current playback pointer position in frames.
+ */
+static snd_pcm_uframes_t
+tascam_playback_pointer(struct snd_pcm_substream *substream)
+{
+	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	u64 pos;
+
+	if (!atomic_read(&tascam->playback_active))
+		return 0;
+
+	guard(spinlock_irqsave)(&tascam->lock);
+	pos = tascam->playback_frames_consumed;
+
+	if (runtime->buffer_size == 0)
+		return 0;
+
+	u64 remainder = do_div(pos, runtime->buffer_size);
+
+	return runtime ? remainder : 0;
+}
+
+/**
+ * tascam_playback_ops - ALSA PCM operations for playback.
+ *
+ * This structure defines the callback functions for playback stream operations,
+ * including open, close, ioctl, hardware parameters, hardware free, prepare,
+ * trigger, and pointer.
+ */
+const struct snd_pcm_ops tascam_playback_ops = {
+	.open = tascam_playback_open,
+	.close = tascam_playback_close,
+	.ioctl = snd_pcm_lib_ioctl,
+	.hw_params = tascam_pcm_hw_params,
+	.hw_free = tascam_pcm_hw_free,
+	.prepare = tascam_playback_prepare,
+	.trigger = tascam_pcm_trigger,
+	.pointer = tascam_playback_pointer,
+};
-- 
2.39.5

On Wed, 13 Aug 2025 15:15:13 +0200,
Šerif Rami wrote:
> 
> +static snd_pcm_uframes_t
> +tascam_capture_pointer(struct snd_pcm_substream *substream)
> +{
> +	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +	u64 pos;
> +
> +	if (!atomic_read(&tascam->capture_active))
> +		return 0;
> +
> +	guard(spinlock_irqsave)(&tascam->lock);
> +	pos = tascam->capture_frames_processed;
> +
> +	if (runtime->buffer_size == 0)
> +		return 0;
> +
> +	u64 remainder = do_div(pos, runtime->buffer_size);
> +
> +	return runtime ? remainder : 0;

If runtime is NULL, it already hits Oops, so this NULL check makes
little sense.

Also, the "u64 remainder" declaration should be put at the beginning
of the function (although nowadays allowed in the middle).
But, judging the code, you don't have to assign but just return
do_div().


> +static snd_pcm_uframes_t
> +tascam_playback_pointer(struct snd_pcm_substream *substream)
> +{
> +	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +	u64 pos;
> +
> +	if (!atomic_read(&tascam->playback_active))
> +		return 0;
> +
> +	guard(spinlock_irqsave)(&tascam->lock);
> +	pos = tascam->playback_frames_consumed;
> +
> +	if (runtime->buffer_size == 0)
> +		return 0;
> +
> +	u64 remainder = do_div(pos, runtime->buffer_size);
> +
> +	return runtime ? remainder : 0;

Ditto.
	

thanks,

Takashi