[PATCH v6 0/2] Add generic serial MIDI driver using serial bus API

[PATCH v6 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 v6:    
- Change compatible "serialmidi" -> serial-midi" 
- Default current-speed to 38400 (closest baud to MIDI standard speed) 
- Appropriately stop reading or writing MIDI if input or output
    _trigger() is called with a parameter of zero, respectively 
- Zero out corresponding triggered state on close to ensure input and
    output closing results in the serial port being closed 
- Fix order of operations in _probe() 
- Remove "DEBUG" literal from debug messages
- Remove unused dt-parsing patch checking for existence of node
- Whitespace / tabbing fixes / improvements

Changes in v5:
- Reword description in dt-binding for clarity
- Change 'speed' dt property to standard 'current-speed'
- Move MIDI output loop onto workqueue (since this could loop quite a while,
    if ALSA provides a continuous stream of bytes)
- Add tx_state bit flags to snd_serial_generic struct
- Safegard critical section in tx_work with atomic bit ops on tx_state
- Switch operations on filemode to use atomic bit ops

Changes in v4:
- Fix regressed typo - Correct 3.84 kBaud -> 38.4 kBaud in DT & Kconfig
  (sorry about spam - noticed after sending v3 and didn't want to let
  the error sit around for too long)

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

 .../bindings/sound/serial-midi.yaml           |  50 +++
 sound/drivers/Kconfig                         |  18 +
 sound/drivers/Makefile                        |   2 +
 sound/drivers/serial-generic.c                | 374 ++++++++++++++++++
 4 files changed, 444 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml
 create mode 100644 sound/drivers/serial-generic.c


base-commit: c5eb0a61238dd6faf37f58c9ce61c9980aaffd7a
-- 
2.33.0

[PATCH v6 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 v6:    
- Change compatible "serialmidi" -> serial-midi" 
- Default current-speed to 38400 (closest baud to MIDI standard speed) 
- Appropriately stop reading or writing MIDI if input or output
    _trigger() is called with a parameter of zero, respectively 
- Zero out corresponding triggered state on close to ensure input and
    output closing results in the serial port being closed 
- Fix order of operations in _probe() 
- Remove "DEBUG" literal from debug messages
- Remove unused dt-parsing patch checking for existence of node
- Whitespace / tabbing fixes / improvements

Changes in v5:
- Reword description in dt-binding for clarity
- Change 'speed' dt property to standard 'current-speed'
- Move MIDI output loop onto workqueue (since this could loop quite a while,
    if ALSA provides a continuous stream of bytes)
- Add tx_state bit flags to snd_serial_generic struct
- Safegard critical section in tx_work with atomic bit ops on tx_state
- Switch operations on filemode to use atomic bit ops

Changes in v4:
- Fix regressed typo - Correct 3.84 kBaud -> 38.4 kBaud in DT & Kconfig
  (sorry about spam - noticed after sending v3 and didn't want to let
  the error sit around for too long)

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

 .../bindings/sound/serial-midi.yaml           |  50 +++
 sound/drivers/Kconfig                         |  18 +
 sound/drivers/Makefile                        |   2 +
 sound/drivers/serial-generic.c                | 374 ++++++++++++++++++
 4 files changed, 444 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml
 create mode 100644 sound/drivers/serial-generic.c


base-commit: c5eb0a61238dd6faf37f58c9ce61c9980aaffd7a
-- 
2.33.0

[PATCH v6 1/2] dt-bindings: sound: Add generic serial MIDI device

[Daniel Kaehn]

Adds dt-binding for a Generic MIDI Interface using a serial device.

Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
---
 .../bindings/sound/serial-midi.yaml           | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml

diff --git a/Documentation/devicetree/bindings/sound/serial-midi.yaml b/Documentation/devicetree/bindings/sound/serial-midi.yaml
new file mode 100644
index 000000000000..74849be01df3
--- /dev/null
+++ b/Documentation/devicetree/bindings/sound/serial-midi.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/serial-midi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Serial MIDI Interface
+
+maintainers:
+  - Daniel Kaehn <kaehndan@gmail.com>
+
+description:
+  Generic MIDI interface using a serial device. This denotes that a serial device is
+  dedicated to MIDI communication, either to an external MIDI device through a DIN5
+  or other connector, or to a known hardwired MIDI controller. This device must be a
+  child node of a serial node.
+
+  Can only be set to use standard baud rates corresponding to supported rates of the
+  parent serial device. If the standard MIDI baud of 31.25 kBaud is needed
+  (as would be the case if interfacing with arbitrary external MIDI devices),
+  configure the clocks of the parent serial device so that a requested baud of 38.4 kBaud
+  resuts in the standard MIDI baud rate, and set the 'current-speed' property to 38400 (default)
+
+properties:
+  compatible:
+    const: serial-midi
+
+  current-speed:
+    description: Baudrate to set the serial port to when this MIDI device is opened.
+    default: 38400
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    serial@7e201400 {
+        midi {
+            compatible = "serial-midi";
+        };
+    };
+    serial@7e201600 {
+        midi {
+            compatible = "serial-midi";
+            current-speed = <115200>;
+        };
+    };
-- 
2.33.0

[PATCH v6 1/2] dt-bindings: sound: Add generic serial MIDI device

[Daniel Kaehn]

Adds dt-binding for a Generic MIDI Interface using a serial device.

Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
---
 .../bindings/sound/serial-midi.yaml           | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml

diff --git a/Documentation/devicetree/bindings/sound/serial-midi.yaml b/Documentation/devicetree/bindings/sound/serial-midi.yaml
new file mode 100644
index 000000000000..74849be01df3
--- /dev/null
+++ b/Documentation/devicetree/bindings/sound/serial-midi.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/serial-midi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Serial MIDI Interface
+
+maintainers:
+  - Daniel Kaehn <kaehndan@gmail.com>
+
+description:
+  Generic MIDI interface using a serial device. This denotes that a serial device is
+  dedicated to MIDI communication, either to an external MIDI device through a DIN5
+  or other connector, or to a known hardwired MIDI controller. This device must be a
+  child node of a serial node.
+
+  Can only be set to use standard baud rates corresponding to supported rates of the
+  parent serial device. If the standard MIDI baud of 31.25 kBaud is needed
+  (as would be the case if interfacing with arbitrary external MIDI devices),
+  configure the clocks of the parent serial device so that a requested baud of 38.4 kBaud
+  resuts in the standard MIDI baud rate, and set the 'current-speed' property to 38400 (default)
+
+properties:
+  compatible:
+    const: serial-midi
+
+  current-speed:
+    description: Baudrate to set the serial port to when this MIDI device is opened.
+    default: 38400
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    serial@7e201400 {
+        midi {
+            compatible = "serial-midi";
+        };
+    };
+    serial@7e201600 {
+        midi {
+            compatible = "serial-midi";
+            current-speed = <115200>;
+        };
+    };
-- 
2.33.0

[PATCH v6 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 | 374 +++++++++++++++++++++++++++++++++
 3 files changed, 394 insertions(+)
 create mode 100644 sound/drivers/serial-generic.c

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);
-- 
2.33.0

[PATCH v6 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 | 374 +++++++++++++++++++++++++++++++++
 3 files changed, 394 insertions(+)
 create mode 100644 sound/drivers/serial-generic.c

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);
-- 
2.33.0

Re: [PATCH v6 1/2] dt-bindings: sound: Add generic serial MIDI device

[Rob Herring]

On Sun, 08 May 2022 22:28:35 -0500, Daniel Kaehn wrote:
> Adds dt-binding for a Generic MIDI Interface using a serial device.
> 
> Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
> ---
>  .../bindings/sound/serial-midi.yaml           | 50 +++++++++++++++++++
>  1 file changed, 50 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Documentation/devicetree/bindings/sound/serial-midi.example.dts:20.25-24.11: Warning (unit_address_vs_reg): /example-0/serial@7e201400: node has a unit name, but no reg or ranges property
Documentation/devicetree/bindings/sound/serial-midi.example.dts:25.25-30.11: Warning (unit_address_vs_reg): /example-0/serial@7e201600: node has a unit name, but no reg or ranges property

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/patch/

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.

Re: [PATCH v6 1/2] dt-bindings: sound: Add generic serial MIDI device

[Rob Herring]

On Sun, 08 May 2022 22:28:35 -0500, Daniel Kaehn wrote:
> Adds dt-binding for a Generic MIDI Interface using a serial device.
> 
> Signed-off-by: Daniel Kaehn <kaehndan@gmail.com>
> ---
>  .../bindings/sound/serial-midi.yaml           | 50 +++++++++++++++++++
>  1 file changed, 50 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/sound/serial-midi.yaml
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Documentation/devicetree/bindings/sound/serial-midi.example.dts:20.25-24.11: Warning (unit_address_vs_reg): /example-0/serial@7e201400: node has a unit name, but no reg or ranges property
Documentation/devicetree/bindings/sound/serial-midi.example.dts:25.25-30.11: Warning (unit_address_vs_reg): /example-0/serial@7e201600: node has a unit name, but no reg or ranges property

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/patch/

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.