[PATCH v3 0/2] Add generic serial MIDI driver using serial bus API

[PATCH v3 0/2] Add generic serial MIDI driver using serial bus API

[Daniel Kaehn]

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.

Changes in v3:
- Replace use of snd_printk() with dev_* alternatives
- Removed unnecessary initialization of err variables
- Replaced instances of `== SERIAL_MODE_NOT_OPENED` with zero check
- Loop on output_write to completely fill output buffer if data available
- Depend on CONFIG_OF in Kconfig
- Replace use of devm_kzalloc() with extra_size allocation in snd_devm_card_new()
- Use module_serdev_device_driver() instead of module_init() and module_exit(0)

Changes in v2:
- Fix 'snd_serial_generic_write_wakeup' missing static keyword 
- Correct 3.125 kBaud > 31.25 kBaud in documentation for MIDI         


The need for this driver arose from a project using a Raspberry Pi4 which
needed to receive and send raw MIDI with low latency. The pl011 UART
used is not compatible with the existing serial MIDI driver made for
u16550-style devices. Using a userspace program such as ttymidi to feed
input from the TTY device to a virtual ALSA MIDI device was functional,
but not ideal.

I am not sure if a MIDI driver needing the mentioned 'hack' to clock
38.4 kBaud down to the standard MIDI baud is permissible in the mainline
kernel, but am submitting nevertheless in case it is useful. To my knowledge,
it doesn't seem that there would be any way for this driver to manually
configure a serial port to 31.25 kBaud using the serial bus API (please 
correct me f I'm wrong). In my use case, I am actually configuring one port
to run at 115.2 kBaud for faster communication with a custom onboard MIDI controller.



Daniel Kaehn (2):
  dt-bindings: sound: Add generic serial MIDI device
  Add generic serial MIDI driver using serial bus API

 .../devicetree/bindings/sound/serialmidi.yaml |  41 +++
 sound/drivers/Kconfig                         |  18 +
 sound/drivers/Makefile                        |   2 +
 sound/drivers/serial-generic.c                | 316 ++++++++++++++++++
 4 files changed, 377 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serialmidi.yaml
 create mode 100644 sound/drivers/serial-generic.c


base-commit: af2d861d4cd2a4da5137f795ee3509e6f944a25b
-- 
2.33.0

[PATCH v3 0/2] Add generic serial MIDI driver using serial bus API

[Daniel Kaehn]

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.

Changes in v3:
- Replace use of snd_printk() with dev_* alternatives
- Removed unnecessary initialization of err variables
- Replaced instances of `== SERIAL_MODE_NOT_OPENED` with zero check
- Loop on output_write to completely fill output buffer if data available
- Depend on CONFIG_OF in Kconfig
- Replace use of devm_kzalloc() with extra_size allocation in snd_devm_card_new()
- Use module_serdev_device_driver() instead of module_init() and module_exit(0)

Changes in v2:
- Fix 'snd_serial_generic_write_wakeup' missing static keyword 
- Correct 3.125 kBaud > 31.25 kBaud in documentation for MIDI         


The need for this driver arose from a project using a Raspberry Pi4 which
needed to receive and send raw MIDI with low latency. The pl011 UART
used is not compatible with the existing serial MIDI driver made for
u16550-style devices. Using a userspace program such as ttymidi to feed
input from the TTY device to a virtual ALSA MIDI device was functional,
but not ideal.

I am not sure if a MIDI driver needing the mentioned 'hack' to clock
38.4 kBaud down to the standard MIDI baud is permissible in the mainline
kernel, but am submitting nevertheless in case it is useful. To my knowledge,
it doesn't seem that there would be any way for this driver to manually
configure a serial port to 31.25 kBaud using the serial bus API (please 
correct me f I'm wrong). In my use case, I am actually configuring one port
to run at 115.2 kBaud for faster communication with a custom onboard MIDI controller.



Daniel Kaehn (2):
  dt-bindings: sound: Add generic serial MIDI device
  Add generic serial MIDI driver using serial bus API

 .../devicetree/bindings/sound/serialmidi.yaml |  41 +++
 sound/drivers/Kconfig                         |  18 +
 sound/drivers/Makefile                        |   2 +
 sound/drivers/serial-generic.c                | 316 ++++++++++++++++++
 4 files changed, 377 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serialmidi.yaml
 create mode 100644 sound/drivers/serial-generic.c


base-commit: af2d861d4cd2a4da5137f795ee3509e6f944a25b
-- 
2.33.0

[PATCH v3 1/2] dt-bindings: sound: Add generic serial MIDI device

[Daniel Kaehn]

Adds dt-binding for snd-serial-generic serial MIDI driver

Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
---
 .../devicetree/bindings/sound/serialmidi.yaml | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serialmidi.yaml

diff --git a/Documentation/devicetree/bindings/sound/serialmidi.yaml b/Documentation/devicetree/bindings/sound/serialmidi.yaml
new file mode 100644
index 000000000000..74f02a9e1190
--- /dev/null
+++ b/Documentation/devicetree/bindings/sound/serialmidi.yaml
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/serialmidi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Serial MIDI Device
+
+maintainers:
+  - Daniel Kaehn <kaehndan@gmail.com>
+
+description: |
+  Generic MIDI interface using a serial device. Can only be set to use standard speeds
+  corresponding to supported baud rates of the underlying serial device. If standard MIDI
+  speed of 31.25 kBaud is needed, configure the clocks of the underlying serial device
+  so that a requested speed of 3.840 kBaud resuts in the standard MIDI baud rate.
+
+properties:
+  compatible:
+    const: serialmidi
+
+  speed:
+    maxItems: 1
+    description: |
+      Speed to set the serial port to when the MIDI device is opened.
+      If not specified, the underlying serial device is allowed to use its configured default speed.
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    serial {
+        midi {
+            compatible = "serialmidi";
+            speed = <38400>;
+        };
+    };
-- 
2.33.0

[PATCH v3 1/2] dt-bindings: sound: Add generic serial MIDI device

[Daniel Kaehn]

Adds dt-binding for snd-serial-generic serial MIDI driver

Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
---
 .../devicetree/bindings/sound/serialmidi.yaml | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serialmidi.yaml

diff --git a/Documentation/devicetree/bindings/sound/serialmidi.yaml b/Documentation/devicetree/bindings/sound/serialmidi.yaml
new file mode 100644
index 000000000000..74f02a9e1190
--- /dev/null
+++ b/Documentation/devicetree/bindings/sound/serialmidi.yaml
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/serialmidi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Serial MIDI Device
+
+maintainers:
+  - Daniel Kaehn <kaehndan@gmail.com>
+
+description: |
+  Generic MIDI interface using a serial device. Can only be set to use standard speeds
+  corresponding to supported baud rates of the underlying serial device. If standard MIDI
+  speed of 31.25 kBaud is needed, configure the clocks of the underlying serial device
+  so that a requested speed of 3.840 kBaud resuts in the standard MIDI baud rate.
+
+properties:
+  compatible:
+    const: serialmidi
+
+  speed:
+    maxItems: 1
+    description: |
+      Speed to set the serial port to when the MIDI device is opened.
+      If not specified, the underlying serial device is allowed to use its configured default speed.
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    serial {
+        midi {
+            compatible = "serialmidi";
+            speed = <38400>;
+        };
+    };
-- 
2.33.0

[PATCH v3 2/2] Add generic serial MIDI driver using serial bus API

[Daniel Kaehn]

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>
---
 sound/drivers/Kconfig          |  18 ++
 sound/drivers/Makefile         |   2 +
 sound/drivers/serial-generic.c | 316 +++++++++++++++++++++++++++++++++
 3 files changed, 336 insertions(+)
 create mode 100644 sound/drivers/serial-generic.c

diff --git a/sound/drivers/Kconfig b/sound/drivers/Kconfig
index ca4cdf666f82..6f58a8531ed8 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 3.84 kBaud will result in the standard speed.
+
+	  Use this devicetree binding to configure serial port mapping
+	  <file:Documentation/devicetree/bindings/sound/serialmidi.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..af1f19db33aa
--- /dev/null
+++ b/sound/drivers/serial-generic.c
@@ -0,0 +1,316 @@
+// 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 << 0)
+#define SERIAL_MODE_OUTPUT_OPEN		(1 << 1)
+#define SERIAL_MODE_INPUT_TRIGGERED	(1 << 2)
+#define SERIAL_MODE_OUTPUT_TRIGGERED	(1 << 3)
+
+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;
+
+	int filemode;		/* open status of file */
+	unsigned int baudrate;
+};
+
+static int snd_serial_generic_ensure_serdev_open(struct snd_serial_generic *drvdata)
+{
+	int err;
+	unsigned int actual_baud;
+
+	if (!drvdata->filemode) {
+		err = serdev_device_open(drvdata->serdev);
+		if (err < 0)
+			return err;
+		if (drvdata->baudrate) {
+			actual_baud = serdev_device_set_baudrate(drvdata->serdev,
+				drvdata->baudrate);
+			if (actual_baud != drvdata->baudrate) {
+				dev_warn(drvdata->card->dev, "snd-serial-generic: requested %d baud for %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, "snd-serial-generic: DEBUG - Opening input for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	drvdata->filemode |= SERIAL_MODE_INPUT_OPEN;
+	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;
+
+	drvdata->filemode &= ~SERIAL_MODE_INPUT_OPEN;
+	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)
+		drvdata->filemode |= SERIAL_MODE_INPUT_TRIGGERED;
+	else
+		drvdata->filemode &= ~SERIAL_MODE_INPUT_TRIGGERED;
+}
+
+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, "snd-serial-generic: DEBUG - Opening output for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	drvdata->filemode |= SERIAL_MODE_OUTPUT_OPEN;
+	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;
+
+	drvdata->filemode &= ~SERIAL_MODE_OUTPUT_OPEN;
+	drvdata->midi_output = NULL;
+	if (!drvdata->filemode)
+		serdev_device_close(drvdata->serdev);
+	return 0;
+};
+
+#define INTERNAL_BUF_SIZE 256
+
+static void snd_serial_generic_output_write(struct snd_rawmidi_substream *substream)
+{
+	static char buf[INTERNAL_BUF_SIZE];
+	int num_bytes;
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	while (!snd_rawmidi_transmit_empty(substream)) {
+		num_bytes = snd_rawmidi_transmit_peek(substream, buf, INTERNAL_BUF_SIZE);
+		num_bytes = serdev_device_write_buf(drvdata->serdev, buf, num_bytes);
+		snd_rawmidi_transmit_ack(substream, num_bytes);
+	}
+}
+
+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)
+		drvdata->filemode |= SERIAL_MODE_OUTPUT_TRIGGERED;
+	else
+		drvdata->filemode &= ~SERIAL_MODE_OUTPUT_TRIGGERED;
+	if (up)
+		snd_serial_generic_output_write(substream);
+}
+
+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,
+};
+
+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 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);
+
+	ret = snd_rawmidi_receive(drvdata->midi_input, buf, count);
+	return ret < 0 ? 0 : ret;
+}
+
+static void snd_serial_generic_write_wakeup(struct serdev_device *serdev)
+{
+	struct snd_serial_generic *drvdata = serdev_device_get_drvdata(serdev);
+
+	if (!snd_rawmidi_transmit_empty(drvdata->midi_output))
+		snd_serial_generic_output_write(drvdata->midi_output);
+}
+
+
+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 void snd_serial_generic_parse_dt(struct serdev_device *serdev,
+				struct snd_serial_generic *drvdata)
+{
+	int err;
+
+	if (serdev->dev.of_node) {
+		err = of_property_read_u32(serdev->dev.of_node, "speed", &drvdata->baudrate);
+		if (err < 0) {
+			dev_warn(drvdata->card->dev,
+				"snd-serial-generic: MIDI device reading of speed DT param failed with error %d, using default baudrate of serial device\n",
+				err);
+			drvdata->baudrate = 0;
+		}
+	} else {
+		dev_info(drvdata->card->dev, "snd-serial-generic: MIDI device speed DT param not set for %s, using default baudrate of serial device\n",
+			drvdata->card->shortname);
+		drvdata->baudrate = 0;
+	}
+}
+
+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);
+
+	err = snd_serial_generic_rmidi(drvdata, 1, 1, &drvdata->rmidi);
+	if (err < 0)
+		return err;
+
+	err = snd_card_register(card);
+
+	if (err < 0)
+		return err;
+
+	serdev_device_set_client_ops(serdev, &snd_serial_generic_serdev_device_ops);
+	serdev_device_set_drvdata(drvdata->serdev, drvdata);
+
+	return 0;
+}
+
+#define SND_SERIAL_GENERIC_DRIVER	"snd-serial-generic"
+
+static const struct of_device_id snd_serial_generic_dt_ids[] = {
+	{ .compatible = "serialmidi" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, snd_serial_generic_dt_ids);
+
+static struct serdev_device_driver snd_serial_generic_driver = {
+	.driver	= {
+		.name		= SND_SERIAL_GENERIC_DRIVER,
+		.of_match_table	= of_match_ptr(snd_serial_generic_dt_ids),
+	},
+	.probe	= snd_serial_generic_probe,
+};
+
+module_serdev_device_driver(snd_serial_generic_driver);
-- 
2.33.0

[PATCH v3 2/2] Add generic serial MIDI driver using serial bus API

[Daniel Kaehn]

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>
---
 sound/drivers/Kconfig          |  18 ++
 sound/drivers/Makefile         |   2 +
 sound/drivers/serial-generic.c | 316 +++++++++++++++++++++++++++++++++
 3 files changed, 336 insertions(+)
 create mode 100644 sound/drivers/serial-generic.c

diff --git a/sound/drivers/Kconfig b/sound/drivers/Kconfig
index ca4cdf666f82..6f58a8531ed8 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 3.84 kBaud will result in the standard speed.
+
+	  Use this devicetree binding to configure serial port mapping
+	  <file:Documentation/devicetree/bindings/sound/serialmidi.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..af1f19db33aa
--- /dev/null
+++ b/sound/drivers/serial-generic.c
@@ -0,0 +1,316 @@
+// 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 << 0)
+#define SERIAL_MODE_OUTPUT_OPEN		(1 << 1)
+#define SERIAL_MODE_INPUT_TRIGGERED	(1 << 2)
+#define SERIAL_MODE_OUTPUT_TRIGGERED	(1 << 3)
+
+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;
+
+	int filemode;		/* open status of file */
+	unsigned int baudrate;
+};
+
+static int snd_serial_generic_ensure_serdev_open(struct snd_serial_generic *drvdata)
+{
+	int err;
+	unsigned int actual_baud;
+
+	if (!drvdata->filemode) {
+		err = serdev_device_open(drvdata->serdev);
+		if (err < 0)
+			return err;
+		if (drvdata->baudrate) {
+			actual_baud = serdev_device_set_baudrate(drvdata->serdev,
+				drvdata->baudrate);
+			if (actual_baud != drvdata->baudrate) {
+				dev_warn(drvdata->card->dev, "snd-serial-generic: requested %d baud for %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, "snd-serial-generic: DEBUG - Opening input for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	drvdata->filemode |= SERIAL_MODE_INPUT_OPEN;
+	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;
+
+	drvdata->filemode &= ~SERIAL_MODE_INPUT_OPEN;
+	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)
+		drvdata->filemode |= SERIAL_MODE_INPUT_TRIGGERED;
+	else
+		drvdata->filemode &= ~SERIAL_MODE_INPUT_TRIGGERED;
+}
+
+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, "snd-serial-generic: DEBUG - Opening output for card %s\n",
+		drvdata->card->shortname);
+
+	err = snd_serial_generic_ensure_serdev_open(drvdata);
+	if (err < 0)
+		return err;
+
+	drvdata->filemode |= SERIAL_MODE_OUTPUT_OPEN;
+	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;
+
+	drvdata->filemode &= ~SERIAL_MODE_OUTPUT_OPEN;
+	drvdata->midi_output = NULL;
+	if (!drvdata->filemode)
+		serdev_device_close(drvdata->serdev);
+	return 0;
+};
+
+#define INTERNAL_BUF_SIZE 256
+
+static void snd_serial_generic_output_write(struct snd_rawmidi_substream *substream)
+{
+	static char buf[INTERNAL_BUF_SIZE];
+	int num_bytes;
+	struct snd_serial_generic *drvdata = substream->rmidi->card->private_data;
+
+	while (!snd_rawmidi_transmit_empty(substream)) {
+		num_bytes = snd_rawmidi_transmit_peek(substream, buf, INTERNAL_BUF_SIZE);
+		num_bytes = serdev_device_write_buf(drvdata->serdev, buf, num_bytes);
+		snd_rawmidi_transmit_ack(substream, num_bytes);
+	}
+}
+
+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)
+		drvdata->filemode |= SERIAL_MODE_OUTPUT_TRIGGERED;
+	else
+		drvdata->filemode &= ~SERIAL_MODE_OUTPUT_TRIGGERED;
+	if (up)
+		snd_serial_generic_output_write(substream);
+}
+
+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,
+};
+
+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 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);
+
+	ret = snd_rawmidi_receive(drvdata->midi_input, buf, count);
+	return ret < 0 ? 0 : ret;
+}
+
+static void snd_serial_generic_write_wakeup(struct serdev_device *serdev)
+{
+	struct snd_serial_generic *drvdata = serdev_device_get_drvdata(serdev);
+
+	if (!snd_rawmidi_transmit_empty(drvdata->midi_output))
+		snd_serial_generic_output_write(drvdata->midi_output);
+}
+
+
+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 void snd_serial_generic_parse_dt(struct serdev_device *serdev,
+				struct snd_serial_generic *drvdata)
+{
+	int err;
+
+	if (serdev->dev.of_node) {
+		err = of_property_read_u32(serdev->dev.of_node, "speed", &drvdata->baudrate);
+		if (err < 0) {
+			dev_warn(drvdata->card->dev,
+				"snd-serial-generic: MIDI device reading of speed DT param failed with error %d, using default baudrate of serial device\n",
+				err);
+			drvdata->baudrate = 0;
+		}
+	} else {
+		dev_info(drvdata->card->dev, "snd-serial-generic: MIDI device speed DT param not set for %s, using default baudrate of serial device\n",
+			drvdata->card->shortname);
+		drvdata->baudrate = 0;
+	}
+}
+
+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);
+
+	err = snd_serial_generic_rmidi(drvdata, 1, 1, &drvdata->rmidi);
+	if (err < 0)
+		return err;
+
+	err = snd_card_register(card);
+
+	if (err < 0)
+		return err;
+
+	serdev_device_set_client_ops(serdev, &snd_serial_generic_serdev_device_ops);
+	serdev_device_set_drvdata(drvdata->serdev, drvdata);
+
+	return 0;
+}
+
+#define SND_SERIAL_GENERIC_DRIVER	"snd-serial-generic"
+
+static const struct of_device_id snd_serial_generic_dt_ids[] = {
+	{ .compatible = "serialmidi" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, snd_serial_generic_dt_ids);
+
+static struct serdev_device_driver snd_serial_generic_driver = {
+	.driver	= {
+		.name		= SND_SERIAL_GENERIC_DRIVER,
+		.of_match_table	= of_match_ptr(snd_serial_generic_dt_ids),
+	},
+	.probe	= snd_serial_generic_probe,
+};
+
+module_serdev_device_driver(snd_serial_generic_driver);
-- 
2.33.0