ALSA: Add generic serial MIDI driver using serial bus API

Generic serial MIDI driver adding support for using serial devices
compatible with the serial bus as raw MIDI devices, allowing using
additional serial devices not compatible with the existing
serial-u16550 driver. Supports only setting standard serial baudrates on
the underlying serial device; however, the underlying serial device can
be configured so that a requested 38.4 kBaud is actually the standard MIDI
31.25 kBaud. Supports DeviceTree configuration.

Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220509145933.1161526-3-kaehndan@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

3 files changed, 394 insertions, 0 deletions

diff --git a/sound/drivers/Kconfig b/sound/drivers/Kconfig
index ca4cdf666f82..be3009746f3a 100644
--- a/sound/drivers/Kconfig
+++ b/sound/drivers/Kconfig
@@ -165,6 +165,24 @@ config SND_SERIAL_U16550
 	  To compile this driver as a module, choose M here: the module
 	  will be called snd-serial-u16550.
 
+config SND_SERIAL_GENERIC
+	tristate "Generic serial MIDI driver"
+	depends on SERIAL_DEV_BUS
+	depends on OF
+	select SND_RAWMIDI
+	help
+	  To include support for mapping generic serial devices as raw
+	  ALSA MIDI devices, say Y here. The driver only supports setting
+	  the serial port to standard baudrates. To attain the standard MIDI
+	  baudrate of 31.25 kBaud, configure the clock of the underlying serial
+	  device so that a requested 38.4 kBaud will result in the standard speed.
+
+	  Use this devicetree binding to configure serial port mapping
+	  <file:Documentation/devicetree/bindings/sound/serial-midi.yaml>
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called snd-serial-generic.
+
 config SND_MPU401
 	tristate "Generic MPU-401 UART driver"
 	select SND_MPU401_UART
diff --git a/sound/drivers/Makefile b/sound/drivers/Makefile
index c0fe4eccdaef..b60303180a1b 100644
--- a/sound/drivers/Makefile
+++ b/sound/drivers/Makefile
@@ -10,6 +10,7 @@ snd-mtpav-objs := mtpav.o
 snd-mts64-objs := mts64.o
 snd-portman2x4-objs := portman2x4.o
 snd-serial-u16550-objs := serial-u16550.o
+snd-serial-generic-objs := serial-generic.o
 snd-virmidi-objs := virmidi.o
 
 # Toplevel Module Dependency
@@ -17,6 +18,7 @@ obj-$(CONFIG_SND_DUMMY) += snd-dummy.o
 obj-$(CONFIG_SND_ALOOP) += snd-aloop.o
 obj-$(CONFIG_SND_VIRMIDI) += snd-virmidi.o
 obj-$(CONFIG_SND_SERIAL_U16550) += snd-serial-u16550.o
+obj-$(CONFIG_SND_SERIAL_GENERIC) += snd-serial-generic.o
 obj-$(CONFIG_SND_MTPAV) += snd-mtpav.o
 obj-$(CONFIG_SND_MTS64) += snd-mts64.o
 obj-$(CONFIG_SND_PORTMAN2X4) += snd-portman2x4.o
diff --git a/sound/drivers/serial-generic.c b/sound/drivers/serial-generic.c
new file mode 100644
index 000000000000..e1f864dc7939
--- /dev/null
+++ b/sound/drivers/serial-generic.c
@@ -0,0 +1,374 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   serial-generic.c
+ *   Copyright (c) by Daniel Kaehn <kaehndan@gmail.com
+ *   Based on serial-u16550.c by Jaroslav Kysela <perex@perex.cz>,
+ *		                 Isaku Yamahata <yamahata@private.email.ne.jp>,
+ *		                 George Hansper <ghansper@apana.org.au>,
+ *		                 Hannu Savolainen
+ *
+ * Generic serial MIDI driver using the serdev serial bus API for hardware interaction
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/serdev.h>
+#include <linux/serial_reg.h>
+#include <linux/slab.h>
+#include <linux/dev_printk.h>
+
+#include <sound/core.h>
+#include <sound/rawmidi.h>
+#include <sound/initval.h>
+
+MODULE_DESCRIPTION("Generic serial MIDI driver");
+MODULE_LICENSE("GPL");
+
+#define SERIAL_MODE_INPUT_OPEN		1
+#define SERIAL_MODE_OUTPUT_OPEN	2
+#define SERIAL_MODE_INPUT_TRIGGERED	3
+#define SERIAL_MODE_OUTPUT_TRIGGERED	4
+
+#define SERIAL_TX_STATE_ACTIVE	1
+#define SERIAL_TX_STATE_WAKEUP	2
+
+struct snd_serial_generic {
+	struct serdev_device *serdev;
+
+	struct snd_card *card;
+	struct snd_rawmidi *rmidi;
+	struct snd_rawmidi_substream *midi_output;
+	struct snd_rawmidi_substream *midi_input;
+
+	unsigned int baudrate;
+
+	unsigned long filemode;		/* open status of file */
+	struct work_struct tx_work;
+	unsigned long tx_state;
+
+};
+
+static void snd_serial_generic_tx_wakeup(struct snd_serial_generic *drvdata)
+{
+	if (test_and_set_bit(SERIAL_TX_STATE_ACTIVE, &drvdata->tx_state))
+		set_bit(SERIAL_TX_STATE_WAKEUP, &drvdata->tx_state);
+
+	schedule_work(&drvdata->tx_work);
+}
+
+#define INTERNAL_BUF_SIZE 256
+
+static void snd_serial_generic_tx_work(struct work_struct *work)
+{
+	static char buf[INTERNAL_BUF_SIZE];
+	int num_bytes;
+	struct snd_serial_generic *drvdata = container_of(work, struct snd_serial_generic,
+						   tx_work);
+	struct snd_rawmidi_substream *substream = drvdata->midi_output;
+
+	clear_bit(SERIAL_TX_STATE_WAKEUP, &drvdata->tx_state);
+
+	while (!snd_rawmidi_transmit_empty(substream)) {
+
+		if (!test_bit(SERIAL_MODE_OUTPUT_OPEN, &drvdata->filemode))
+			break;
+
+		num_bytes = snd_rawmidi_transmit_peek(substream, buf, INTERNAL_BUF_SIZE);
+		num_bytes = serdev_device_write_buf(drvdata->serdev, buf, num_bytes);
+
+		if (!num_bytes)
+			break;
+
+		snd_rawmidi_transmit_ack(substream, num_bytes);
+
+		if (!test_bit(SERIAL_TX_STATE_WAKEUP, &drvdata->tx_state))
+			break;
+	}
+
+	clear_bit(SERIAL_TX_STATE_ACTIVE, &drvdata->tx_state);
+}
+
+static void snd_serial_generic_write_wakeup(struct serdev_device *serdev)
+{
+	struct snd_serial_generic *drvdata = serdev_device_get_drvdata(serdev);
+
+	snd_serial_generic_tx_wakeup(drvdata);
+}
+
+static int snd_serial_generic_receive_buf(struct serdev_device *serdev,
+				const unsigned char *buf, size_t count)
+{
+	int ret;
+	struct snd_serial_generic *drvdata = serdev_device_get_drvdata(serdev);
+
+	if (!test_bit(SERIAL_MODE_INPUT_OPEN, &drvdata->filemode))
+		return 0;
+
+	ret = snd_rawmidi_receive(drvdata->midi_input, buf, count);
+	return ret < 0 ? 0 : ret;
+}
+
+static const struct serdev_device_ops snd_serial_generic_serdev_device_ops = {
+	.receive_buf = snd_serial_generic_receive_buf,
+	.write_wakeup = snd_serial_generic_write_wakeup
+};
+
+static int snd_serial_generic_ensure_serdev_open(struct snd_serial_generic *drvdata)
+{
+	int err;
+	unsigned int actual_baud;
+
+	if (drvdata->filemode)
+		return 0;
+
+	dev_dbg(drvdata->card->dev, "Opening serial port for card %s\n",
+		drvdata->card->shortname);
+	err = serdev_device_open(drvdata->serdev);
+	if (err < 0)
+		return err;
+
+	actual_baud = serdev_device_set_baudrate(drvdata->serdev,
+		drvdata->baudrate);
+	if (actual_baud != drvdata->baudrate) {
+		dev_warn(drvdata->card->dev, "requested %d baud for card %s but it was actually set to %d\n",
+			drvdata->baudrate, drvdata->card->shortname, actual_baud);
+	}
+
+	return 0;
+}
+
+static int snd_serial_generic_input_open(struct snd_rawmidi_substream *substream)
+{
+	int err;
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	dev_dbg(drvdata->card->dev, "Opening input for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	set_bit(SERIAL_MODE_INPUT_OPEN, &drvdata->filemode);
+	drvdata->midi_input = substream;
+	return 0;
+}
+
+static int snd_serial_generic_input_close(struct snd_rawmidi_substream *substream)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	dev_dbg(drvdata->card->dev, "Closing input for card %s\n",
+		drvdata->card->shortname);
+
+	clear_bit(SERIAL_MODE_INPUT_OPEN, &drvdata->filemode);
+	clear_bit(SERIAL_MODE_INPUT_TRIGGERED, &drvdata->filemode);
+
+	drvdata->midi_input = NULL;
+
+	if (!drvdata->filemode)
+		serdev_device_close(drvdata->serdev);
+	return 0;
+}
+
+static void snd_serial_generic_input_trigger(struct snd_rawmidi_substream *substream,
+					int up)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	if (up)
+		set_bit(SERIAL_MODE_INPUT_TRIGGERED, &drvdata->filemode);
+	else
+		clear_bit(SERIAL_MODE_INPUT_TRIGGERED, &drvdata->filemode);
+}
+
+static int snd_serial_generic_output_open(struct snd_rawmidi_substream *substream)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+	int err;
+
+	dev_dbg(drvdata->card->dev, "Opening output for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	set_bit(SERIAL_MODE_OUTPUT_OPEN, &drvdata->filemode);
+
+	drvdata->midi_output = substream;
+	return 0;
+};
+
+static int snd_serial_generic_output_close(struct snd_rawmidi_substream *substream)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	dev_dbg(drvdata->card->dev, "Closing output for card %s\n",
+		drvdata->card->shortname);
+
+	clear_bit(SERIAL_MODE_OUTPUT_OPEN, &drvdata->filemode);
+	clear_bit(SERIAL_MODE_OUTPUT_TRIGGERED, &drvdata->filemode);
+
+	if (!drvdata->filemode)
+		serdev_device_close(drvdata->serdev);
+
+	drvdata->midi_output = NULL;
+
+	return 0;
+};
+
+static void snd_serial_generic_output_trigger(struct snd_rawmidi_substream *substream,
+					 int up)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	if (up)
+		set_bit(SERIAL_MODE_OUTPUT_TRIGGERED, &drvdata->filemode);
+	else
+		clear_bit(SERIAL_MODE_OUTPUT_TRIGGERED, &drvdata->filemode);
+
+	if (up)
+		snd_serial_generic_tx_wakeup(drvdata);
+}
+
+static void snd_serial_generic_output_drain(struct snd_rawmidi_substream *substream)
+{
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	/* Flush any pending characters */
+	serdev_device_write_flush(drvdata->serdev);
+	cancel_work_sync(&drvdata->tx_work);
+}
+
+static const struct snd_rawmidi_ops snd_serial_generic_output = {
+	.open =		snd_serial_generic_output_open,
+	.close =	snd_serial_generic_output_close,
+	.trigger =	snd_serial_generic_output_trigger,
+	.drain =	snd_serial_generic_output_drain,
+};
+
+static const struct snd_rawmidi_ops snd_serial_generic_input = {
+	.open =		snd_serial_generic_input_open,
+	.close =	snd_serial_generic_input_close,
+	.trigger =	snd_serial_generic_input_trigger,
+};
+
+static void snd_serial_generic_parse_dt(struct serdev_device *serdev,
+				struct snd_serial_generic *drvdata)
+{
+	int err;
+
+	err = of_property_read_u32(serdev->dev.of_node, "current-speed",
+		&drvdata->baudrate);
+	if (err < 0) {
+		dev_dbg(drvdata->card->dev,
+			"MIDI device reading of current-speed DT param failed with error %d, using default of 38400\n",
+			err);
+		drvdata->baudrate = 38400;
+	}
+
+}
+
+static void snd_serial_generic_substreams(struct snd_rawmidi_str *stream, int dev_num)
+{
+	struct snd_rawmidi_substream *substream;
+
+	list_for_each_entry(substream, &stream->substreams, list) {
+		sprintf(substream->name, "Serial MIDI %d-%d", dev_num, substream->number);
+	}
+}
+
+static int snd_serial_generic_rmidi(struct snd_serial_generic *drvdata,
+				int outs, int ins, struct snd_rawmidi **rmidi)
+{
+	struct snd_rawmidi *rrawmidi;
+	int err;
+
+	err = snd_rawmidi_new(drvdata->card, drvdata->card->driver, 0,
+				outs, ins, &rrawmidi);
+
+	if (err < 0)
+		return err;
+
+	snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_INPUT,
+				&snd_serial_generic_input);
+	snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_OUTPUT,
+				&snd_serial_generic_output);
+	strcpy(rrawmidi->name, drvdata->card->shortname);
+
+	snd_serial_generic_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT],
+					drvdata->serdev->ctrl->nr);
+	snd_serial_generic_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_INPUT],
+					drvdata->serdev->ctrl->nr);
+
+	rrawmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
+			       SNDRV_RAWMIDI_INFO_INPUT |
+			       SNDRV_RAWMIDI_INFO_DUPLEX;
+
+	if (rmidi)
+		*rmidi = rrawmidi;
+	return 0;
+}
+
+static int snd_serial_generic_probe(struct serdev_device *serdev)
+{
+	struct snd_card *card;
+	struct snd_serial_generic *drvdata;
+	int err;
+
+	err  = snd_devm_card_new(&serdev->dev, SNDRV_DEFAULT_IDX1,
+				SNDRV_DEFAULT_STR1, THIS_MODULE,
+				sizeof(struct snd_serial_generic), &card);
+
+	if (err < 0)
+		return err;
+
+	strcpy(card->driver, "SerialMIDI");
+	sprintf(card->shortname, "SerialMIDI-%d", serdev->ctrl->nr);
+	sprintf(card->longname, "Serial MIDI device at serial%d", serdev->ctrl->nr);
+
+	drvdata = card->private_data;
+
+	drvdata->serdev = serdev;
+	drvdata->card = card;
+
+	snd_serial_generic_parse_dt(serdev, drvdata);
+
+	INIT_WORK(&drvdata->tx_work, snd_serial_generic_tx_work);
+
+	err = snd_serial_generic_rmidi(drvdata, 1, 1, &drvdata->rmidi);
+	if (err < 0)
+		return err;
+
+	serdev_device_set_client_ops(serdev, &snd_serial_generic_serdev_device_ops);
+	serdev_device_set_drvdata(drvdata->serdev, drvdata);
+
+	err = snd_card_register(card);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static const struct of_device_id snd_serial_generic_dt_ids[] = {
+	{ .compatible = "serial-midi" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, snd_serial_generic_dt_ids);
+
+static struct serdev_device_driver snd_serial_generic_driver = {
+	.driver	= {
+		.name		= "snd-serial-generic",
+		.of_match_table	= of_match_ptr(snd_serial_generic_dt_ids),
+	},
+	.probe	= snd_serial_generic_probe,
+};
+
+module_serdev_device_driver(snd_serial_generic_driver);