Serial MIDI driver for PL011 - as found on BCM2835 hardware

On Wed, 2014-10-22 at 08:51 +0200, Takashi Iwai wrote:
> At Wed, 22 Oct 2014 09:24:35 +1100,
> Kim Taylor wrote:
> > 
> > On Tue, 2014-10-21 at 09:20 +0200, Daniel Mack wrote:
> > > Hi,
> > > 
> > > Thanks for sharing this!
> > > 
> > > On 10/21/2014 01:40 AM, Kim Taylor wrote:
> > > > I've written a driver for raw MIDI using the PL011. It is obviously
> > > > based on the snd-serial-u16550 module, with a couple of improvements:
> > > >
> > > >  - I've implemented a drain() callback.
> > > > 
> > > >  - I've also implemented a half duplex mode based on a timer callback
> > > > which was necessary for reliable communication with my eMagic Unitor 8
> > > > hardware. (Testing with a serial link to other hardware shows that the
> > > > full duplex mode is also working.)
> > > 
> > > So I guess you could patch the existing driver to make it work for your
> > > use case, right? I haven't looked at the code in detail, but from what
> > > you describe, that should be possible.
> > 
> > I'm not sure about that. As it uses a different UART chip, there is a
> > new probe() function, it uses memory mapped I/O, instead of i386
> > inb/outb, it gathers information from the ARM AMBA bus...
> > 
> > The only things that would remain unchanged are the output_trigger() and
> > output_write() functions. One possibility might be to abstract out all
> > read/write operations using function pointers, however, I believe that
> > the new driver is different enough to constitute a new module.
> > 
> > Or maybe there should be a third module (for example snd-serial-core,
> > containing any common functions, exporting them to both
> > snd-serial-u16550 and snd-serial-pl011?
> 
> Yes, that sounds good.  Of course, it depends on the volume they can
> share.  If there are so few, no big merit to split to modules.  Let's
> see.
> 
> 
> Takashi
>
Here's the patch. In line with Takashi's comment, I've not split the
modules. There is not much to be shared. Recent changes include using a
hrtimer instead of a timer for half duplex mode.

I've been using the driver for a couple of weeks now and it appears to
be stable.

diff -uprN sound-orig/sound/drivers/Makefile
sound-new/sound/drivers/Makefile

--- sound-orig/sound/drivers/Makefile	2014-11-07 11:24:19.000000000
+1100
+++ sound-new/sound/drivers/Makefile	2014-11-07 11:16:49.000000000 +1100
@@ -9,6 +9,7 @@ snd-mtpav-objs := mtpav.o
 snd-mts64-objs := mts64.o
 snd-portman2x4-objs := portman2x4.o
 snd-serial-u16550-objs := serial-u16550.o
+snd-serial-pl011-objs := serial-pl011.o
 snd-virmidi-objs := virmidi.o
 snd-ml403-ac97cr-objs := ml403-ac97cr.o pcm-indirect2.o
 
@@ -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-$(CONFIG_SND_SERIAL_PL011) += snd-serial-pl011.o
 obj-$(CONFIG_SND_MTPAV) += snd-mtpav.o
 obj-$(CONFIG_SND_MTS64) += snd-mts64.o
 obj-$(CONFIG_SND_PORTMAN2X4) += snd-portman2x4.o
diff -uprN sound-orig/sound/drivers/serial-pl011.c
sound-new/sound/drivers/serial-pl011.c
--- sound-orig/sound/drivers/serial-pl011.c	1970-01-01
10:00:00.000000000 +1000
+++ sound-new/sound/drivers/serial-pl011.c	2014-11-07 11:32:04.000000000
+1100
@@ -0,0 +1,1089 @@
+/*
+ *   serial-pl011.c
+ *   Copyright (c) by Jaroslav Kysela <perex@perex.cz>,
+ *                    Isaku Yamahata <yamahata@private.email.ne.jp>,
+ *		      George Hansper <ghansper@apana.org.au>,
+ *		      Hannu Savolainen
+ *		      Kim Taylor
+ *
+ *   This code is based on the code from serial-u16550.
+ *
+ *   This program is free software; you can redistribute it and/or
modify
+ *   it under the terms of the GNU General Public License as published
by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA
+ *
+ * Sat Mar 31 17:27:57 PST 2001 tim.mann@compaq.com 
+ *      Added support for the Midiator MS-124T and for the MS-124W in
+ *      Single Addressed (S/A) or Multiple Burst (M/B) mode, with
+ *      power derived either parasitically from the serial port or
+ *      from a separate power supply.
+ *
+ *      More documentation can be found in serial-u16550.txt.
+ */
+
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/ioport.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/rawmidi.h>
+#include <sound/initval.h>
+
+#include <linux/amba/bus.h>
+#include <linux/amba/serial.h>
+#include <linux/pinctrl/consumer.h>
+#include <linux/clk.h>
+#include <linux/jiffies.h>
+
+#include <asm/io.h>
+
+MODULE_DESCRIPTION("MIDI serial pl011");
+MODULE_LICENSE("GPL");
+MODULE_SUPPORTED_DEVICE("{{ALSA, MIDI serial pl011}}");
+
+#define SNDRV_SERIAL_SOUNDCANVAS 0 /* Roland Soundcanvas; F5 NN selects
part */
+#define SNDRV_SERIAL_MS124T 1      /* Midiator MS-124T */
+#define SNDRV_SERIAL_MS124W_SA 2   /* Midiator MS-124W in S/A mode */
+#define SNDRV_SERIAL_MS124W_MB 3   /* Midiator MS-124W in M/B mode */
+#define SNDRV_SERIAL_GENERIC 4     /* Generic Interface */
+#define SNDRV_SERIAL_MAX_ADAPTOR SNDRV_SERIAL_GENERIC
+static char *adaptor_names[] = {
+	"Soundcanvas",
+        "MS-124T",
+	"MS-124W S/A",
+	"MS-124W M/B",
+	"Generic"
+};
+
+#define SNDRV_SERIAL_NORMALBUFF 0 /* Normal blocking buffer operation
*/
+#define SNDRV_SERIAL_DROPBUFF   1 /* Non-blocking discard operation */
+#define SNDRV_SERIAL_NOTHROTTLE 0
+#define SNDRV_SERIAL_NORTSCTS 0
+#define SNDRV_SERIAL_DEFAULT_FIFO 16
+#define TIMER_ATTEMPTS_LIMIT 255
+
+static int speed = 115200; /* 9600,19200,38400,57600,115200 */
+static int outs = 1;	 /* 1 to 16 */
+static int ins = 1;	/* 1 to 16 */
+static int adaptor = SNDRV_SERIAL_GENERIC;
+static bool droponfull = SNDRV_SERIAL_NORMALBUFF;
+static bool throttle_tx = SNDRV_SERIAL_NOTHROTTLE;
+static int throttle_delay = 1000;
+static int fifo_limit = SNDRV_SERIAL_DEFAULT_FIFO;
+static bool flow_control = SNDRV_SERIAL_NORTSCTS;
+
+module_param(speed, int, 0444);
+MODULE_PARM_DESC(speed, "Speed in bauds.");
+module_param(outs, int, 0444);
+MODULE_PARM_DESC(outs, "Number of MIDI outputs.");
+module_param(ins, int, 0444);
+MODULE_PARM_DESC(ins, "Number of MIDI inputs.");
+module_param(droponfull, bool, 0444);
+MODULE_PARM_DESC(droponfull, "Flag to enable drop-on-full buffer
mode");
+module_param(throttle_tx, bool, 0444);
+MODULE_PARM_DESC(throttle_tx, "Do not continuously fill TX FIFO");
+module_param(throttle_delay, int, 0444);
+MODULE_PARM_DESC(throttle_delay, "Time in us between each TX write");
+module_param(flow_control, bool, 0444);
+MODULE_PARM_DESC(flow_control, "Use RTS/CTS flow control");
+module_param(fifo_limit, int, 0444);
+MODULE_PARM_DESC(fifo_limit, "Maximum TX bytes per write");
+
+module_param(adaptor, int, 0444);
+MODULE_PARM_DESC(adaptor, "Type of adaptor.");
+
+/*#define SNDRV_SERIAL_MS124W_MB_NOCOMBO 1*/  /* Address outs as 0-3
instead of bitmap */
+
+#define SNDRV_SERIAL_MAX_OUTS	16		/* max 64, min 16 */
+#define SNDRV_SERIAL_MAX_INS	16		/* max 64, min 16 */
+
+#define TX_BUFF_SIZE		(1<<15)		/* Must be 2^n */
+#define TX_BUFF_MASK		(TX_BUFF_SIZE - 1)
+
+#define AMBA_ISR_PASS_LIMIT	256
+
+#define SERIAL_MODE_NOT_OPENED 		(0)
+#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_uart_pl011 {
+	struct amba_device *dev;
+	struct snd_card *card;
+	struct snd_rawmidi *rmidi;
+	struct snd_rawmidi_substream *midi_output[SNDRV_SERIAL_MAX_OUTS];
+	struct snd_rawmidi_substream *midi_input[SNDRV_SERIAL_MAX_INS];
+
+	int filemode;		/* open status of file */
+
+	spinlock_t open_lock;
+	wait_queue_head_t drain_wait;
+	int draining;
+
+	int irq;
+
+	void __iomem *membase;
+	unsigned long mapbase;
+	struct resource *res_base;
+
+	struct clk *clk;
+	unsigned long clk_rate;
+	unsigned int speed;
+
+	/* parameter for using of write loop */
+	short int fifo_limit;
+        short int fifo_count;
+
+	/* type of adaptor */
+	int adaptor;
+
+	/* inputs */
+	int prev_in;
+	unsigned char rstatus;
+
+	/* outputs */
+	int prev_out;
+	unsigned char prev_status[SNDRV_SERIAL_MAX_OUTS];
+
+	/* write buffer and its writing/reading position */
+	unsigned char tx_buff[TX_BUFF_SIZE];
+	int buff_in_count;
+        int buff_in;
+        int buff_out;
+        int drop_on_full;
+	int throttle_tx;
+	int flow_control;
+	ktime_t throttle_delay;
+
+	int timer_running;
+	u16 control_reg;
+	enum {
+		TX_IDLE,
+		TX_BLOCK_RX,
+		TX_BUSY,
+	} tx_state;
+	int tx_attempts;
+	struct hrtimer buffer_timer;
+};
+
+static inline void snd_uart_pl011_stop_rx(struct snd_uart_pl011 *uart)
+{
+	writew(uart->control_reg & ~UART011_CR_RTS, uart->membase +
UART011_CR);
+}
+
+static inline void snd_uart_pl011_start_rx(struct snd_uart_pl011 *uart)
+{
+	writew(uart->control_reg | UART011_CR_RTS, uart->membase +
UART011_CR);
+}
+
+/* This macro is only used in snd_uart_pl011_io_loop */
+static inline void snd_uart_pl011_buffer_output(struct snd_uart_pl011
*uart)
+{
+	unsigned short buff_out = uart->buff_out;
+	if (uart->buff_in_count > 0) {
+		writeb(uart->tx_buff[buff_out], uart->membase + UART01x_DR);
+		uart->fifo_count++;
+		buff_out++;
+		buff_out &= TX_BUFF_MASK;
+		uart->buff_out = buff_out;
+		uart->buff_in_count--;
+	}
+}
+
+static inline int snd_uart_pl011_write_fifo_timer(struct snd_uart_pl011
* uart)
+{
+	/* Check CTS - FIFO is empty */
+	if (!uart->flow_control ||
+			readw(uart->membase + UART01x_FR) & UART01x_FR_CTS) {
+		while (uart->fifo_count < uart->fifo_limit
+			&& uart->buff_in_count > 0)
+			snd_uart_pl011_buffer_output(uart); 
+	
+		uart->tx_state = TX_BUSY;
+		if (unlikely(uart->draining))
+			wake_up(&uart->drain_wait);
+		return 1;
+	}
+	return 0;
+}
+
+static inline void snd_uart_pl011_start_timer(struct snd_uart_pl011
*uart)
+{
+        if (!uart->timer_running) {
+		if (uart->flow_control) {
+			snd_uart_pl011_stop_rx(uart);
+			uart->tx_state = TX_BLOCK_RX;
+			uart->tx_attempts = TIMER_ATTEMPTS_LIMIT;
+		} else {
+			snd_uart_pl011_write_fifo_timer(uart);
+		}
+		hrtimer_start(&uart->buffer_timer, uart->throttle_delay,
+				HRTIMER_MODE_REL);
+		uart->timer_running = 1;
+        }
+}
+
+static inline void snd_uart_pl011_del_timer(struct snd_uart_pl011
*uart)
+{
+        hrtimer_cancel(&uart->buffer_timer);
+        uart->timer_running = 0;
+}
+
+/* This loop should be called with interrupts disabled
+ * We don't want to interrupt this, 
+ * as we're already handling an interrupt 
+ *
+ * PL011 interrupts that must be serviced (and cleared):
+ * UART011_RXIC	    (RX FIFO becoming full)
+ * UART011_TXIC	    (TX FIFO becoming empty)
+ * UART011_RTIC	    (RX timeout reached)
+ */
+static void snd_uart_pl011_io_loop(struct snd_uart_pl011 * uart)
+{
+	unsigned char c;
+	int substream;
+	int pass_counter = AMBA_ISR_PASS_LIMIT;
+
+	/* recall previous stream */
+	substream = uart->prev_in;
+    
+	/* Read Loop */
+	while (!(readw(uart->membase + UART01x_FR) & UART01x_FR_RXFE)) {
+		/* while receive data ready */
+		c = readb(uart->membase + UART01x_DR);
+
+		/* keep track of last status byte */
+		if (c & 0x80)
+			uart->rstatus = c;
+
+		/* handle stream switch */
+		if (uart->adaptor == SNDRV_SERIAL_GENERIC) {
+			if (uart->rstatus == 0xf5) {
+				if (c <= SNDRV_SERIAL_MAX_INS && c > 0)
+					substream = c - 1;
+				if (c != 0xf5)
+					/* prevent future bytes from being
+					   interpreted as streams */
+					uart->rstatus = 0;
+			} else if ((uart->filemode & SERIAL_MODE_INPUT_OPEN)
+				   && uart->midi_input[substream])
+				snd_rawmidi_receive(uart->midi_input[substream],
+						    &c, 1);
+		} else if ((uart->filemode & SERIAL_MODE_INPUT_OPEN) &&
+			   uart->midi_input[substream])
+			snd_rawmidi_receive(uart->midi_input[substream], &c, 1);
+
+		if (readw(uart->membase + UART01x_FR) & UART011_FR_RXFF)
+			snd_printk(KERN_WARNING
+				   "%s: Overrun on device at 0x%lx\n",
+			       uart->rmidi->name, uart->mapbase);
+
+		if (pass_counter-- == 0) break;
+	}
+
+	/* remember the last stream */
+	uart->prev_in = substream;
+
+	if (uart->throttle_tx) return;
+
+	/* Check write status, if we get a TX fifo interrupt,
+	 * it's possible that there are still 2 bytes of data
+	 * in the FIFO */
+	if (readw(uart->membase + UART011_MIS) & UART011_TXIS) {
+		writew(UART011_TXIC, uart->membase + UART011_ICR);
+		uart->fifo_count = 2;
+		if (unlikely(uart->draining)) wake_up(&uart->drain_wait);
+	}
+
+	if (readw(uart->membase + UART01x_FR) & UART011_FR_TXFE)
+		uart->fifo_count = 0;
+
+	/* Write loop */
+	while (uart->fifo_count < uart->fifo_limit /* Can we write ? */
+		&& uart->buff_in_count > 0)	/* Do we want to? */
+		snd_uart_pl011_buffer_output(uart);
+}
+
+static irqreturn_t snd_uart_pl011_interrupt(int irq, void *dev_id)
+{
+	struct snd_uart_pl011 *uart;
+
+	uart = dev_id;
+	spin_lock(&uart->open_lock);
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED) {
+		spin_unlock(&uart->open_lock);
+		return IRQ_NONE;
+	}
+
+	snd_uart_pl011_io_loop(uart);
+	spin_unlock(&uart->open_lock);
+	return IRQ_HANDLED;
+}
+
+static enum hrtimer_restart snd_uart_pl011_buffer_timer(struct hrtimer
*handle)
+{
+        struct snd_uart_pl011 *uart = 
+		container_of(handle, struct snd_uart_pl011, buffer_timer);
+	enum hrtimer_restart restart = HRTIMER_NORESTART;
+	int double_delay = 0;
+
+        spin_lock(&uart->open_lock);
+
+	switch (uart->tx_state) {
+	    case TX_IDLE:
+		snd_uart_pl011_stop_rx(uart);
+		uart->tx_attempts = TIMER_ATTEMPTS_LIMIT;
+		uart->tx_state = TX_BLOCK_RX;
+		restart = HRTIMER_RESTART;
+		break;
+
+	    case TX_BLOCK_RX:
+		/* Write FIFO, reschedule if necessary */
+		if (snd_uart_pl011_write_fifo_timer(uart)) {
+			restart = HRTIMER_RESTART;
+		} else {
+			/* If the cable becomes disconnected, we may never get 
+			 * CTS. Therefore limit the number of times we call the
+			 * timer */
+			if (uart->tx_attempts--) restart = HRTIMER_RESTART;
+			else uart->tx_state = TX_IDLE;
+		}
+
+		break;
+
+	    case TX_BUSY:
+		if (readw(uart->membase + UART01x_FR) & UART01x_FR_BUSY) {
+			/* Still writing, reschedule */
+			restart = HRTIMER_RESTART;
+		} else {
+			/* Finished writing allow receive */
+			uart->fifo_count = 0;
+			if (uart->flow_control) {
+				double_delay = 1;
+				uart->tx_state = TX_IDLE;
+				snd_uart_pl011_start_rx(uart);
+			} else {
+				uart->tx_state = TX_BLOCK_RX;
+			}
+			if (uart->buff_in_count > 0) {
+				restart = HRTIMER_RESTART;
+			}
+		}
+		break;
+	}
+
+	if (restart == HRTIMER_RESTART) {
+		hrtimer_forward_now(&uart->buffer_timer,
+			double_delay ? ktime_add(uart->throttle_delay, 
+				uart->throttle_delay) : uart->throttle_delay);
+	} else
+		uart->timer_running = 0;
+
+        spin_unlock(&uart->open_lock);
+
+	return restart;
+}
+
+static int snd_uart_pl011_detect(struct snd_uart_pl011 *uart)
+{
+	int ok = 0;
+	u16 status;
+	int timeout = 1000;
+
+	writew(0, uart->membase + UART011_IMSC);    /* Disable interrupts */
+
+	writew(UART01x_CR_UARTEN
+	     | UART011_CR_TXE
+	     | UART011_CR_LBE
+	     | UART011_CR_RXE
+	     , uart->membase + UART011_CR);
+
+	writew(0, uart->membase + UART011_FBRD);
+	writew(1, uart->membase + UART011_IBRD);
+	writew(0, uart->membase + UART011_LCRH);
+	writew(0x55, uart->membase + UART01x_DR);
+	while (timeout &&
+		    (readw(uart->membase + UART01x_FR) & UART01x_FR_BUSY)) {
+		timeout--;
+		barrier();
+	}
+	status = readw(uart->membase + UART01x_DR) & 0xff;
+	writew(0xffff, uart->membase + UART011_ICR);	/* Clear interrupts */
+	
+	/* Loopback with WLEN == 5 turns 0x55 into 0x15 */
+	if (status == 0x15) ok = 1;
+
+	return ok;
+}
+
+static void snd_uart_pl011_do_open(struct snd_uart_pl011 * uart)
+{
+	unsigned int quot;
+	u16 reg;
+
+	/* Initialize basic variables */
+	uart->buff_in_count = 0;
+	uart->buff_in = 0;
+	uart->buff_out = 0;
+	uart->fifo_count = 0;
+	uart->tx_state = TX_IDLE;
+
+	writew(UART01x_CR_UARTEN	/* Enable UART */
+	     | UART011_CR_TXE		/* Enable UART TX */
+	     | UART011_CR_RXE		/* Enable UART RX */
+	     , uart->membase + UART011_CR);
+
+	uart->clk_rate = clk_get_rate(uart->clk);
+	quot = DIV_ROUND_CLOSEST(uart->clk_rate * 4, uart->speed);
+
+	writew(quot & 0x3f, uart->membase + UART011_FBRD);
+	writew(quot >> 6, uart->membase + UART011_IBRD);
+
+	writew(UART01x_LCRH_FEN		/* Enable FIFOs */
+	     | UART01x_LCRH_WLEN_8	/* 8 Bit words, 1 Stop, No Parity */
+	     , uart->membase + UART011_LCRH);	/* FIFO Control Register */
+
+	writew(UART011_IFLS_RX2_8 /* Set RX FIFO trigger at 4-bytes */
+	     | UART011_IFLS_TX1_8 /* Set TX FIFO trigger at 2-bytes */
+	     , uart->membase + UART011_IFLS);
+
+	reg = readw(uart->membase + UART011_CR);
+	switch (uart->adaptor) {
+	default:
+		reg |=	UART011_CR_RTS
+			/* Hardware RTS unless throttling*/
+		    | (uart->throttle_tx ? 0 : UART011_CR_RTSEN)	
+			/* Hardware CTS unless throttling */
+		    | (uart->throttle_tx ? 0 : UART011_CR_CTSEN);
+		writew(reg, uart->membase + UART011_CR);
+		break;
+	case SNDRV_SERIAL_MS124W_SA:
+	case SNDRV_SERIAL_MS124W_MB:
+		/* FIXME: MS-124W can draw power from RTS and DTR if they
+		   are in opposite states. */ 
+		break;
+	case SNDRV_SERIAL_MS124T:
+		/* FIXME: MS-124T can draw power from RTS and/or DTR (preferably
+		   both) if they are both asserted. */
+		break;
+	}
+
+	uart->control_reg = reg;
+
+	writew(UART011_RXIC /* Clear corresponting interrupts */
+	     | UART011_TXIC
+	     | UART011_RTIC
+	     , uart->membase + UART011_ICR);
+
+	if (uart->adaptor == SNDRV_SERIAL_MS124W_SA) {
+		/* FIXME: Enable RX data and Modem Status */
+	} else if (uart->adaptor == SNDRV_SERIAL_GENERIC) {
+		writew(UART011_RXIM	/* Enable RX FIFO interrupt */
+		     | UART011_RTIM	/* Enable RX timeout interrupt */
+			/* Enable TX FIFO if not using throttling */
+		     | (uart->throttle_tx ? 0 : UART011_TXIM)
+		     , uart->membase + UART011_IMSC);
+	} else {
+		/* FIXME: Enable RX data and THRI */
+	}
+}
+
+static void snd_uart_pl011_do_close(struct snd_uart_pl011 * uart)
+{
+	writew(0, uart->membase + UART011_IMSC); /* Interrupt enable Register
*/
+	writew(0xffff, uart->membase + UART011_ICR);
+
+	switch (uart->adaptor) {
+	default:
+		/* Disable everything */
+		writew(0, uart->membase + UART011_CR); 
+		break;
+	case SNDRV_SERIAL_MS124W_SA:
+	case SNDRV_SERIAL_MS124W_MB:
+		/* FIXME: MS-124W can draw power from RTS and DTR if they
+		   are in opposite states; leave it powered. */ 
+		break;
+	case SNDRV_SERIAL_MS124T:
+		/* FIXME: MS-124T can draw power from RTS and/or DTR (preferably
+		   both) if they are both asserted; leave it powered. */
+		break;
+	}
+
+}
+
+static int snd_uart_pl011_input_open(struct snd_rawmidi_substream
*substream)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED)
+		snd_uart_pl011_do_open(uart);
+	uart->filemode |= SERIAL_MODE_INPUT_OPEN;
+	uart->midi_input[substream->number] = substream;
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+	return 0;
+}
+
+static int snd_uart_pl011_input_close(struct snd_rawmidi_substream
*substream)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	uart->filemode &= ~SERIAL_MODE_INPUT_OPEN;
+	uart->midi_input[substream->number] = NULL;
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED)
+		snd_uart_pl011_do_close(uart);
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+	return 0;
+}
+
+static void snd_uart_pl011_input_trigger(struct snd_rawmidi_substream
*substream,
+					int up)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	if (up)
+		uart->filemode |= SERIAL_MODE_INPUT_TRIGGERED;
+	else
+		uart->filemode &= ~SERIAL_MODE_INPUT_TRIGGERED;
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+}
+
+static int snd_uart_pl011_output_open(struct snd_rawmidi_substream
*substream)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED)
+		snd_uart_pl011_do_open(uart);
+	uart->filemode |= SERIAL_MODE_OUTPUT_OPEN;
+	uart->midi_output[substream->number] = substream;
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+	return 0;
+};
+
+static int snd_uart_pl011_output_close(struct snd_rawmidi_substream
*substream)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	uart->filemode &= ~SERIAL_MODE_OUTPUT_OPEN;
+	uart->midi_output[substream->number] = NULL;
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED)
+		snd_uart_pl011_do_close(uart);
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+	return 0;
+};
+
+static inline int snd_uart_pl011_buffer_can_write(struct snd_uart_pl011
*uart,
+						 int Num)
+{
+	if (uart->buff_in_count + Num < TX_BUFF_SIZE)
+		return 1;
+	else
+		return 0;
+}
+
+static inline int snd_uart_pl011_write_buffer(struct snd_uart_pl011
*uart,
+					     unsigned char byte)
+{
+	unsigned short buff_in = uart->buff_in;
+	if (uart->buff_in_count < TX_BUFF_SIZE) {
+		uart->tx_buff[buff_in] = byte;
+		buff_in++;
+		buff_in &= TX_BUFF_MASK;
+		uart->buff_in = buff_in;
+		uart->buff_in_count++;
+		if (uart->throttle_tx)
+			snd_uart_pl011_start_timer(uart);
+		return 1;
+	} else
+		return 0;
+}
+
+static int snd_uart_pl011_output_byte(struct snd_uart_pl011 *uart,
+				     struct snd_rawmidi_substream *substream,
+				     unsigned char midi_byte)
+{
+	if ((uart->buff_in_count == 0) && !uart->throttle_tx) {
+	        /* Tx Buffer Empty - try to write immediately */
+		if (readw(uart->membase + UART01x_FR) & UART011_FR_TXFE) {
+		        uart->fifo_count = 1;
+			writeb(midi_byte, uart->membase + UART01x_DR);
+		} else {
+		        if (uart->fifo_count < uart->fifo_limit) {
+			        uart->fifo_count++;
+				writeb(midi_byte, uart->membase + UART01x_DR);
+			} else {
+			        /* Cannot write (buffer empty) -
+				 * put char in buffer */
+				snd_uart_pl011_write_buffer(uart, midi_byte);
+			}
+		}
+	} else {
+		if (!snd_uart_pl011_write_buffer(uart, midi_byte)) {
+			snd_printk(KERN_WARNING
+				   "%s: Buffer overrun on device at 0x%lx\n",
+				   uart->rmidi->name, uart->mapbase);
+			return 0;
+		}
+	}
+	return 1;
+}
+
+static void snd_uart_pl011_output_write(struct snd_rawmidi_substream
*substream)
+{
+	unsigned char midi_byte, addr_byte;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+	char first;
+	static unsigned long lasttime = 0;
+	
+	/* Interrupts are disabled during the updating of the tx_buff,
+	 * since it is 'bad' to have two processes updating the same
+	 * variables (ie buff_in & buff_out)
+	 */
+
+	if (uart->adaptor == SNDRV_SERIAL_MS124W_MB) {
+		while (1) {
+			/* buffer full? */
+			/* in this mode we need two bytes of space */
+			if (uart->buff_in_count > TX_BUFF_SIZE - 2)
+				break;
+			if (snd_rawmidi_transmit(substream, &midi_byte, 1) != 1)
+				break;
+#ifdef SNDRV_SERIAL_MS124W_MB_NOCOMBO
+			/* select exactly one of the four ports */
+			addr_byte = (1 << (substream->number + 4)) | 0x08;
+#else
+			/* select any combination of the four ports */
+			addr_byte = (substream->number << 4) | 0x08;
+			/* ...except none */
+			if (addr_byte == 0x08)
+				addr_byte = 0xf8;
+#endif
+			snd_uart_pl011_output_byte(uart, substream, addr_byte);
+			/* send midi byte */
+			snd_uart_pl011_output_byte(uart, substream, midi_byte);
+		}
+	} else {
+		first = 0;
+		while (snd_rawmidi_transmit_peek(substream, &midi_byte, 1) == 1) {
+			/* Also send F5 after 3 seconds with no data
+			 * to handle device disconnect */
+			if (first == 0 &&
+			    (uart->adaptor == SNDRV_SERIAL_SOUNDCANVAS ||
+			     uart->adaptor == SNDRV_SERIAL_GENERIC) &&
+			    (uart->prev_out != substream->number ||
+			     time_after(jiffies, lasttime + 3*HZ))) {
+
+				if (snd_uart_pl011_buffer_can_write(uart, 3)) {
+					/* Roland Soundcanvas part selection */
+					/* If this substream of the data is
+					 * different previous substream
+					 * in this uart, send the change part
+					 * event
+					 */
+					uart->prev_out = substream->number;
+					/* change part */
+					snd_uart_pl011_output_byte(uart, substream,
+								  0xf5);
+					/* data */
+					snd_uart_pl011_output_byte(uart, substream,
+								  uart->prev_out + 1);
+					/* If midi_byte is a data byte,
+					 * send the previous status byte */
+					if (midi_byte < 0x80 &&
+					    uart->adaptor == SNDRV_SERIAL_SOUNDCANVAS)
+						snd_uart_pl011_output_byte(uart, substream,
uart->prev_status[uart->prev_out]);
+				} else if (!uart->drop_on_full)
+					break;
+
+			}
+
+			/* send midi byte */
+			if (!snd_uart_pl011_output_byte(uart, substream, midi_byte) &&
+			    !uart->drop_on_full )
+				break;
+
+			if (midi_byte >= 0x80 && midi_byte < 0xf0)
+				uart->prev_status[uart->prev_out] = midi_byte;
+			first = 1;
+
+			snd_rawmidi_transmit_ack( substream, 1 );
+		}
+		lasttime = jiffies;
+	}
+}
+
+static void snd_uart_pl011_output_trigger(struct snd_rawmidi_substream
*substream,
+					 int up)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+	if (up) {
+		uart->filemode |= SERIAL_MODE_OUTPUT_TRIGGERED;
+		snd_uart_pl011_output_write(substream);
+	} else {
+		uart->filemode &= ~SERIAL_MODE_OUTPUT_TRIGGERED;
+		snd_uart_pl011_del_timer(uart);
+	}
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+}
+
+static void snd_uart_pl011_output_drain(struct snd_rawmidi_substream
*substream)
+{
+	unsigned long flags;
+	struct snd_uart_pl011 *uart = substream->rmidi->private_data;
+	DEFINE_WAIT(wait);
+	long timeout;
+
+	spin_lock_irqsave(&uart->open_lock, flags);
+
+	if (uart->filemode == SERIAL_MODE_NOT_OPENED) {
+		spin_unlock_irqrestore(&uart->open_lock, flags);
+		return;
+	}
+
+	if (uart->buff_in_count || uart->fifo_count) {
+		uart->draining++;
+		do {
+			timeout = msecs_to_jiffies(50);
+			prepare_to_wait(&uart->drain_wait, &wait,
+					TASK_UNINTERRUPTIBLE);
+			spin_unlock_irqrestore(&uart->open_lock, flags);
+			timeout = schedule_timeout(timeout);
+			spin_lock_irqsave(&uart->open_lock, flags);
+		} while ((uart->buff_in_count || uart->fifo_count) && timeout);
+		uart->draining = 0;
+		finish_wait(&uart->drain_wait, &wait);
+	}
+	spin_unlock_irqrestore(&uart->open_lock, flags);
+}
+
+static struct snd_rawmidi_ops snd_uart_pl011_output =
+{
+	.open =		snd_uart_pl011_output_open,
+	.close =	snd_uart_pl011_output_close,
+	.trigger =	snd_uart_pl011_output_trigger,
+	.drain =	snd_uart_pl011_output_drain,
+};
+
+static struct snd_rawmidi_ops snd_uart_pl011_input =
+{
+	.open =		snd_uart_pl011_input_open,
+	.close =	snd_uart_pl011_input_close,
+	.trigger =	snd_uart_pl011_input_trigger,
+};
+
+static int snd_uart_pl011_free(struct snd_uart_pl011 *uart)
+{
+	if (uart->irq >= 0)
+		free_irq(uart->irq, uart);
+	if (!IS_ERR(uart->clk) && uart->clk) clk_disable_unprepare(uart->clk);
+	if (uart->dev) pinctrl_pm_select_sleep_state(&uart->dev->dev);
+	release_and_free_resource(uart->res_base);
+	kfree(uart);
+	return 0;
+};
+
+static int snd_uart_pl011_dev_free(struct snd_device *device)
+{
+	struct snd_uart_pl011 *uart = device->device_data;
+	return snd_uart_pl011_free(uart);
+}
+
+static int snd_uart_pl011_create(struct snd_card *card,
+				struct amba_device *devptr,
+				unsigned int speed,
+				int adaptor,
+				int droponfull,
+				int throttle_tx,
+				int throttle_delay,
+				int flow_control,
+				int fifo_limit,
+				struct snd_uart_pl011 **ruart)
+{
+	static struct snd_device_ops ops = {
+		.dev_free =	snd_uart_pl011_dev_free,
+	};
+	struct snd_uart_pl011 *uart;
+	int err;
+	void __iomem *membase;
+
+
+	if ((uart = kzalloc(sizeof(*uart), GFP_KERNEL)) == NULL)
+		return -ENOMEM;
+
+	uart->irq = -1;
+	uart->res_base = request_mem_region(devptr->res.start, 
+			resource_size(&devptr->res), "Serial MIDI");
+
+	if (uart->res_base == NULL) {
+		snd_printk(KERN_ERR "pl011: can't grab port\n");
+		return -EBUSY;
+	}
+	
+	membase = devm_ioremap(&devptr->dev, devptr->res.start,
+				    resource_size(&devptr->res));
+
+	if (!membase) {
+		snd_printk(KERN_ERR "pl011: ioremap error\n");
+		snd_uart_pl011_free(uart);
+		return -ENOMEM;
+	}
+
+	uart->clk = devm_clk_get(&devptr->dev, NULL);
+	if (IS_ERR(uart->clk)) {
+		snd_printk(KERN_ERR "pl011: unable to get clock resource\n");
+		snd_uart_pl011_free(uart);
+		return -ENODEV;
+	}
+
+	clk_prepare_enable(uart->clk);
+
+	uart->adaptor = adaptor;
+	uart->card = card;
+	spin_lock_init(&uart->open_lock);
+	uart->membase = membase;
+	uart->mapbase = devptr->res.start;
+	uart->drop_on_full = droponfull;
+	uart->throttle_tx = throttle_tx;
+	uart->throttle_delay = ns_to_ktime(throttle_delay * 1000);
+	uart->flow_control = flow_control;
+	uart->fifo_limit = fifo_limit;
+	uart->speed = speed;
+	uart->prev_out = -1;
+	memset(uart->prev_status, 0x80,
+			sizeof(unsigned char) * SNDRV_SERIAL_MAX_OUTS);
+	hrtimer_init(&uart->buffer_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        uart->buffer_timer.function = snd_uart_pl011_buffer_timer;
+
+	if (snd_uart_pl011_detect(uart) == 0) {
+		snd_printk(KERN_ERR "no UART detected\n");
+		snd_uart_pl011_free(uart);
+		return -ENODEV;
+	}
+
+	if (request_irq(devptr->irq[0], snd_uart_pl011_interrupt,
+				0, "Serial MIDI", uart)) {
+		snd_printk(KERN_ERR "unable to request IRQ\n");
+		snd_uart_pl011_free(uart);
+		return -ENODEV;
+	}
+	uart->irq = devptr->irq[0];
+
+	init_waitqueue_head(&uart->drain_wait);
+
+	snd_printk(KERN_INFO "Detected PL011 at 0x%lx using irq: %i\n",
+			uart->mapbase, uart->irq);
+
+	/* Register device */
+	if ((err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, uart, &ops)) < 0)
{
+		snd_uart_pl011_free(uart);
+		return err;
+	}
+
+	/* FIXME: CTS/RTS pins */
+	uart->dev = devptr;
+	pinctrl_pm_select_default_state(&uart->dev->dev);
+
+	switch (uart->adaptor) {
+	case SNDRV_SERIAL_MS124W_SA:
+	case SNDRV_SERIAL_MS124W_MB:
+		/* FIXME: MS-124W can draw power from RTS and DTR if they
+		   are in opposite states. */ 
+		break;
+	case SNDRV_SERIAL_MS124T:
+		/* FIXME: MS-124T can draw power from RTS and/or DTR (preferably
+		   both) if they are asserted. */
+		break;
+	default:
+		break;
+	}
+
+	if (ruart)
+		*ruart = uart;
+
+	return 0;
+}
+
+static void snd_uart_pl011_substreams(struct snd_rawmidi_str *stream)
+{
+	struct snd_rawmidi_substream *substream;
+
+	list_for_each_entry(substream, &stream->substreams, list) {
+		sprintf(substream->name, "Serial MIDI %d", substream->number + 1);
+	}
+}
+
+static int snd_uart_pl011_rmidi(struct snd_uart_pl011 *uart, int
device,
+			       int outs, int ins,
+			       struct snd_rawmidi **rmidi)
+{
+	struct snd_rawmidi *rrawmidi;
+	int err;
+
+	err = snd_rawmidi_new(uart->card, "UART Serial MIDI", device,
+			      outs, ins, &rrawmidi);
+	if (err < 0)
+		return err;
+	snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_INPUT,
+			    &snd_uart_pl011_input);
+	snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_OUTPUT,
+			    &snd_uart_pl011_output);
+	strcpy(rrawmidi->name, "Serial MIDI");
+
snd_uart_pl011_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT]);
+
snd_uart_pl011_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_INPUT]);
+	rrawmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
+			       SNDRV_RAWMIDI_INFO_INPUT |
+			       SNDRV_RAWMIDI_INFO_DUPLEX;
+	rrawmidi->private_data = uart;
+	if (rmidi)
+		*rmidi = rrawmidi;
+	return 0;
+}
+
+static int snd_serial_probe(struct amba_device *devptr,
+		const struct amba_id *id)
+{
+	struct snd_card *card;
+	struct snd_uart_pl011 *uart;
+	int err;
+
+	switch (adaptor) {
+	case SNDRV_SERIAL_SOUNDCANVAS:
+		ins = 1;
+		break;
+	case SNDRV_SERIAL_MS124T:
+	case SNDRV_SERIAL_MS124W_SA:
+		outs = 1;
+		ins = 1;
+		break;
+	case SNDRV_SERIAL_MS124W_MB:
+		outs = 16;
+		ins = 1;
+		break;
+	case SNDRV_SERIAL_GENERIC:
+		break;
+	default:
+		snd_printk(KERN_ERR
+			   "Adaptor type is out of range 0-%d (%d)\n",
+			   SNDRV_SERIAL_MAX_ADAPTOR, adaptor);
+		return -ENODEV;
+	}
+
+	if (outs < 1 || outs > SNDRV_SERIAL_MAX_OUTS) {
+		snd_printk(KERN_ERR
+			   "Count of outputs is out of range 1-%d (%d)\n",
+			   SNDRV_SERIAL_MAX_OUTS, outs);
+		return -ENODEV;
+	}
+
+	if (ins < 1 || ins > SNDRV_SERIAL_MAX_INS) {
+		snd_printk(KERN_ERR
+			   "Count of inputs is out of range 1-%d (%d)\n",
+			   SNDRV_SERIAL_MAX_INS, ins);
+		return -ENODEV;
+	}
+
+	err  = snd_card_create(-1, NULL, THIS_MODULE, 0, &card);
+	if (err < 0)
+		return err;
+
+	strcpy(card->driver, "Serial");
+	strcpy(card->shortname, "Serial MIDI (PL011)");
+
+	if ((err = snd_uart_pl011_create(card, devptr,
+					speed,
+					adaptor,
+					droponfull,
+					throttle_tx,
+					throttle_delay,
+					flow_control,
+					fifo_limit,
+					&uart)) < 0)
+		goto _err;
+
+	err = snd_uart_pl011_rmidi(uart, 0, outs, ins, &uart->rmidi);
+	if (err < 0)
+		goto _err;
+
+	sprintf(card->longname, "%s [%s] at %#lx, irq %d",
+		card->shortname,
+		adaptor_names[uart->adaptor],
+		(unsigned long) uart->membase,
+		uart->irq);
+
+	snd_card_set_dev(card, &devptr->dev);
+
+	if ((err = snd_card_register(card)) < 0)
+		goto _err;
+
+	amba_set_drvdata(devptr, card);
+	return 0;
+
+ _err:
+	snd_card_free(card);
+	return err;
+}
+
+static int snd_serial_remove(struct amba_device *devptr)
+{
+	snd_card_free(amba_get_drvdata(devptr));
+	return 0;
+}
+
+#define SND_SERIAL_DRIVER	"snd_serial_pl011"
+
+static struct amba_id snd_serial_ids[] = {
+	{
+		.id     = 0x00041011,
+		.mask   = 0x000fffff,
+	},
+	{ 0, 0 },
+};
+
+static struct amba_driver snd_serial_driver = {
+	.drv = {
+		.name	= SND_SERIAL_DRIVER,
+	},
+	.id_table	= snd_serial_ids,
+	.probe		= snd_serial_probe,
+	.remove		= snd_serial_remove,
+};
+
+static int __init alsa_card_serial_init(void)
+{
+	snd_printk(KERN_INFO "snd-serial-pl011: PL011 based MIDI device\n");
+	return amba_driver_register(&snd_serial_driver);
+}
+
+static void __exit alsa_card_serial_exit(void)
+{
+	amba_driver_unregister(&snd_serial_driver);
+}
+
+module_init(alsa_card_serial_init)
+module_exit(alsa_card_serial_exit)


Serial MIDI driver for PL011 - as found on BCM2835 hardware

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