Re: [PATCH 2.6.16-git] [SERIAL] Adds DCC(JTAG) serial and the console emulation support

[Russell King]

On Wed, Mar 29, 2006 at 04:11:25PM +0900, Hyok S. Choi wrote:
> diff --git a/drivers/serial/dcc.c b/drivers/serial/dcc.c

Some comments on this driver below.

> new file mode 100644
> index 0000000..d73ccf6
> --- /dev/null
> +++ b/drivers/serial/dcc.c
> @@ -0,0 +1,550 @@
> +/*
> + *  linux/drivers/serial/dcc.c
> + *
> + *  serial port emulation driver for the JTAG DCC Terminal.
> + *
> + * DCC(JTAG1) protocol version for JTAG ICE/ICD Debuggers:
> + * 	Copyright (C) 2003, 2004, 2005 Hyok S. Choi (hyok.choi@xxxxxxxxxxx)
> + * 	SAMSUNG ELECTRONICS Co.,Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + *  Changelog:
> + *   Oct-2003 Hyok S. Choi	Created
> + *   Feb-2004 Hyok S. Choi 	Updated for serial_core.c and 2.6 kernel
> + *   Apr-2004 Hyok S. Choi 	xmit_string_CR added
> + *   Mar-2005 Hyok S. Choi	renamed from T32 to DCC
> + *
> + */
> +
> +#include <linux/config.h>
> +#include <linux/module.h>
> +#include <linux/tty.h>
> +#include <linux/ioport.h>
> +#include <linux/init.h>
> +#include <linux/serial.h>
> +#include <linux/console.h>
> +#include <linux/sysrq.h>
> +#include <linux/tty_flip.h>
> +#include <linux/major.h>
> +
> +#include <asm/io.h>
> +#include <asm/irq.h>
> +
> +#include <linux/serial_core.h>
> +
> +/*
> + * if real irq interrupt used for receiving character,
> + * uncomment below line. Unless polling method id used.
> + */
> +//#define DCC_IRQ_USED
> +
> +#ifndef  DCC_IRQ_USED
> +static struct work_struct dcc_poll_task;
> +static void dcc_poll(void *data);
> +#endif
> +
> +#define UART_NR			1	/* we have only one JTAG port */
> +
> +#define SERIAL_DCC_NAME		"ttyJ"
> +#define SERIAL_DCC_MAJOR	4
> +#define SERIAL_DCC_MINOR	64

Is it really a good idea to re-use the same major and minor numbers that
are used for 8250?  What if you want to use DCC with a board that has
8250-based serial ports on as well?

> +
> +static int __inline__ __check_JTAG_RX_FLAG(void)

"static inline int" please.

> +{
> +	int __ret=0;
> +	__asm__ __volatile__(
> +		"	mrc		p14, 0, %0, c0, c0 	@ read comms control reg\n"
> +		"	and		%0, %0, #1		@ jtag read buffer status"
> +		: "=r" (__ret)
> +		);
> +
> +	/* if   __ret 	== 0 : no input yet
> +				== 1 : a character pending */

Wouldn't it be clearer to have:

static inline u32 read_dcc_status(void)
{
	u32 status;

	asm("mrc p14, 0, %0, c0, c0" : "=r" (status));

	return status;
}

and if you want to check the RX flag in the rest of the code:

	if (read_dcc_status() & DCC_STAT_RX) {
		/* do pending character stuff */
	}

?

> +	return __ret;	
> +}
> +
> +static void __inline__ __get_JTAG_RX(volatile char *p)
> +{
> +	__asm__ __volatile__(
> +		"	mrc		p14, 0, r3, c1, c0 	@ read comms data reg to r5\n"
> +		"	strb 		r3, 	[%0]		@ str a char"
> +		: /* no output */
> +		: "r" (p)
> +		: "r3",  "memory");
> +}

Ditto comments above.  The only use of this I can find is:

		__get_JTAG_RX(&ch);

and it's crying out to be:

static inline char dcc_getchar(void)
{
	char c;

	asm("mrc p14, 0, %0, c1, c0" : "=r" (c));

	return c;
}

...

		ch = dcc_getchar();

Also, a write_dcc_char(char c) would be useful.

> +static int __inline__ __check_JTAG_TX_FLAG(void)
> +{
> +	int __ret=0;
> +	__asm__ __volatile__(
> +		"	mrc		p14, 0, %0, c0, c0 	@ read comms control reg\n"
> +		"	and 		%0, %0, #2		@ the read buffer status"
> +		: "=r" (__ret)
> +		);
> +
> +	/* if   __ret 	== 0 : tx is available
> +				== 2 : tx busy */
> +	return __ret;	
> +}

Same comments as for __check_JTAG_RX_FLAG().

> +
> +void xmit_string(char *p, int len)
> +{
> +#ifndef CONFIG_JTAG_DCC_OUTPUT_DISABLE
> +	/*
> +		r0 = string	; string address
> +		r1 = 2		; state check bit (write)
> +		r4 = *string	; character
> +		r7 = 0		; count
> +	*/
> +	__asm__ __volatile__(
> +		"	mov r7, #0\n"
> +		"1: 	mrc	p14, 0, r3, c0, c0 	@ read comms control reg\n"
> +		"	and r3, r3, #2			@ the write buffer status\n"
> +		"	cmp r3, #2			@ is it available?\n"
> +		"	beq 1b				@ is not, wait till then\n"
> +		"	ldrb r4, [%0]			@ load a char\n"
> +		"	mcr p14, 0, r4, c1, c0		@ write it\n"
> +		"	add %0, %0, #1			@ str address increase one\n"
> +		"	add r7, r7, #1			@ count increase\n"
> +		"	cmp r7, %1			@ compare with str length\n"
> +		"	bne 1b				@ if it is not yet, loop"
> +		: /* no output register */
> +		: "r" (p), "r" (len)
> +		: "r7", "r3", "r4");
> +#endif
> +}

Does this really need to be written all in assembly?
Shouldn't it be declared static?

Wouldn't something like the following be better?

static void dcc_putchar(struct uart_port *port, char c)
{
	while (read_dcc_status() & DCC_STAT_TX_FULL)
		cpu_relax();
	write_dcc_char(c);
}

static void xmit_string(struct uart_port *port, const char *p, int len)
{
	for (; len; len--, p++)
		dcc_putchar(port, *p);
}

> +
> +void xmit_string_CR(char *p, int len)
> +{
> +#ifndef CONFIG_JTAG_DCC_OUTPUT_DISABLE
> +	/*
> +		r0 = string	; string address
> +		r1 = 2		; state check bit (write)
> +		r4 = *string	; character
> +		r7 = 0		; count
> +	*/
> +	__asm__ __volatile__(
> +		"	mov r7, #0\n"
> +		"	ldrb r4, [%0]			@ load a char\n"
> +		"1: 	mrc	p14, 0, r3, c0, c0 	@ read comms control reg\n"
> +		"	and r3, r3, #2			@ the write buffer status\n"
> +		"	cmp r3, #2			@ is it available?\n"
> +		"	beq 1b				@ is not, wait till then\n"
> +		"	mcr p14, 0, r4, c1, c0		@ write it\n"
> +		"	cmp r4, #0x0a			@ is it LF?\n"
> +		"	bne 2f				@ if it is not, continue\n"
> +		"	mov r4, #0x0d			@ set the CR\n"
> +		"	b   1b				@ loop for writing CR\n"			
> +		"2:	ldrb r4, [%0, #1]!		@ load a char\n"
> +		"	add r7, r7, #1			@ count increase\n"
> +		"	cmp r7, %1			@ compare with str length\n"
> +		"	bne 1b				@ if it is not yet, loop"
> +		: /* no output register */
> +		: "r" (p), "r" (len)
> +		: "r7", "r3", "r4");
> +#endif
> +}

No need - use uart_console_write() for this, which will do the LF -> CRLF
translation for you.  All you need to do is to supply a function to do
the individual character based writing.  You can pass dcc_putchar()
as the putchar function (which is why I wrote xmit_string that way
above.)

> +
> +
> +static void
> +dcc_stop_tx(struct uart_port *port)
> +{
> +}
> +
> +static inline void
> +dcc_transmit_buffer(struct uart_port *port)
> +{
> +	struct circ_buf *xmit = &port->info->xmit;
> +

Blank line not required.

> +	int pendings = uart_circ_chars_pending(xmit);
> +
> +	if(pendings + xmit->tail > UART_XMIT_SIZE)
> +	{

Interesting indentation style mix.

> +		xmit_string(&(xmit->buf[xmit->tail]), UART_XMIT_SIZE - xmit->tail);
> +		xmit_string(&(xmit->buf[0]), xmit->head);
> +	} else
> +		xmit_string(&(xmit->buf[xmit->tail]), pendings);
> +	
> +	xmit->tail = (xmit->tail + pendings) & (UART_XMIT_SIZE-1);
> +        port->icount.tx += pendings;

Tabs vs spaces indentation.  Please use a consistent indentation style.

> +
> +	if (uart_circ_empty(xmit))
> +		dcc_stop_tx(port); 

dcc_stop_tx itself is empty, so this doesn't serve a useful purpose.

> +}
> +
> +static inline void
> +dcc_transmit_x_char(struct uart_port *port)
> +{
> +	xmit_string(&port->x_char, 1);

Another potential user of dcc_putchar().

> +	port->icount.tx++;
> +	port->x_char = 0;
> +}
> +
> +static void
> +dcc_start_tx(struct uart_port *port)
> +{
> +    dcc_transmit_buffer(port);
> +}
> +
> +static void
> +dcc_stop_rx(struct uart_port *port)
> +{
> +}
> +
> +static void
> +dcc_enable_ms(struct uart_port *port)
> +{
> +}

Maybe call all the empty functions which take just a uart_port

static void dcc_dummy(struct uart_port *port)
{
}

and use it in the uart_ops structure as appropriate.

> +
> +static inline void
> +dcc_rx_chars(struct uart_port *port)
> +{
> +	unsigned char ch;
> +	struct tty_struct *tty = port->info->tty;
> +
> +	/*
> +	 * check input.
> +	 * checking JTAG flag is better to resolve the status test.
> +	 * incount is NOT used for JTAG1 protocol.
> +	 */
> +
> +	if (__check_JTAG_RX_FLAG())
> +		/* if   __ret 	== 0 : no input yet
> +					== 1 : a character pending */

	if (read_dcc_status() & DCC_STAT_RX) {

> +	{
> +		/* for JTAG 1 protocol, incount is always 1. */
> +		__get_JTAG_RX(&ch);

		ch = dcc_getchar();

> +
> +		if (tty) {
> +			tty_insert_flip_char(tty, ch, TTY_NORMAL);
> +			port->icount.rx++;
> +			tty_flip_buffer_push(tty);
> +		}
> +	}
> +}
> +
> +static inline void
> +dcc_overrun_chars(struct uart_port *port)
> +{
> +	port->icount.overrun++;
> +}
> +
> +static inline void
> +dcc_tx_chars(struct uart_port *port)
> +{
> +	struct circ_buf *xmit = &port->info->xmit;
> +
> +	if (port->x_char) {
> +		dcc_transmit_x_char(port);
> +		return; 
> +	}
> +
> +	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
> +		dcc_stop_tx(port);
> +		return;
> +	}

If we're using interrupt mode, given that dcc_stop_tx() is empty, how
do we stop spinning on the transmit interrupt?

> +
> +	dcc_transmit_buffer(port);
> +
> +	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> +		uart_write_wakeup(port);
> +}
> +
> +#ifdef DCC_IRQ_USED /* real IRQ used */
> +static irqreturn_t
> +dcc_int(int irq, void *dev_id, struct pt_regs *regs)
> +{
> +	struct uart_port *port = dev_id;
> +	int handled = 0;
> +
> +	spin_lock(&port->lock);
> +	
> +	dcc_rx_chars(port);
> +	dcc_tx_chars(port);
> +
> +	handled = 1;
> +	spin_unlock(&port->lock);
> +	
> +	return IRQ_RETVAL(handled);
> +}
> +
> +#else /* emulation by scheduled work */
> +static void
> +dcc_poll(void *data)
> +{
> +	struct uart_port *port = data;
> +
> +	spin_lock(&port->lock);
> +	
> +	dcc_rx_chars(port);
> +	dcc_tx_chars(port);
> +
> +	schedule_delayed_work(&dcc_poll_task, 1);
> +
> +	spin_unlock(&port->lock);
> +	
> +}
> +#endif /* end of DCC_IRQ_USED */
> +
> +static unsigned int
> +dcc_tx_empty(struct uart_port *port)
> +{
> +	return TIOCSER_TEMT;
> +}
> +
> +static unsigned int
> +dcc_get_mctrl(struct uart_port *port)
> +{
> +	return 0;

Should return TIOCM_CTS | TIOCM_DSR | TIOCM_CD if control lines aren't
implemented.

> +}
> +
> +static void
> +dcc_set_mctrl(struct uart_port *port, unsigned int mctrl)
> +{
> +}
> +
> +static void
> +dcc_break_ctl(struct uart_port *port, int break_state)
> +{
> +}
> +
> +static int dcc_startup(struct uart_port *port)
> +{
> +#ifdef DCC_IRQ_USED /* real IRQ used */
> +	int retval;
> +
> +	/* Allocate the IRQ */
> +	retval = request_irq(port->irq, dcc_int, SA_INTERRUPT,
> +			     "serial_dcc", port);
> +	if (retval)
> +		return retval;
> +#else /* emulation */
> +	/* Initialize the work, and shcedule it. */
> +	INIT_WORK(&dcc_poll_task, dcc_poll, port);
> +	schedule_delayed_work(&dcc_poll_task, 1);
> +#endif
> +
> +	return 0;
> +}
> +
> +static void dcc_shutdown(struct uart_port *port)
> +{

Shouldn't the dcc_poll_task be stopped somehow here?

> +}
> +
> +static void
> +dcc_set_termios(struct uart_port *port, struct termios *termios,
> +		   struct termios *old)
> +{
> +#ifdef DCC_IRQ_USED
> +	unsigned long flags;
> +#endif
> +	unsigned int baud, quot;
> +
> +	/*
> +	 * We don't support parity, stop bits, or anything other
> +	 * than 8 bits, so clear these termios flags.
> +	 */
> +	termios->c_cflag &= ~(CSIZE | CSTOPB | PARENB | PARODD | CREAD);
> +	termios->c_cflag |= CS8;
> +
> +	/*
> +	 * We don't appear to support any error conditions either.
> +	 */
> +	termios->c_iflag &= ~(INPCK | IGNPAR | IGNBRK | BRKINT);
> +
> +	/*
> +	 * Ask the core to calculate the divisor for us.
> +	 */
> +	baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16); 
> +	quot = uart_get_divisor(port, baud);
> +
> +#ifdef DCC_IRQ_USED
> +	spin_lock_irqsave(&port->lock, flags);
> +#endif
> +
> +	uart_update_timeout(port, termios->c_cflag, baud);
> +
> +#ifdef DCC_IRQ_USED
> +	spin_unlock_irqrestore(&port->lock, flags);
> +#endif
> +}
> +
> +static const char *dcc_type(struct uart_port *port)
> +{
> +	return port->type == PORT_DCC_JTAG1 ? "DCC" : NULL;
> +}
> +
> +static void dcc_release_port(struct uart_port *port)
> +{
> +}
> +
> +static int dcc_request_port(struct uart_port *port)
> +{
> +	return 0;
> +}
> +
> +/*
> + * Configure/autoconfigure the port.
> + */
> +static void dcc_config_port(struct uart_port *port, int flags)
> +{
> +        if (flags & UART_CONFIG_TYPE) {
> +                port->type = PORT_DCC_JTAG1;
> +                dcc_request_port(port);
> +        }
> +}
> +        
> +/*      
> + * verify the new serial_struct (for TIOCSSERIAL).
> + */     
> +static int dcc_verify_port(struct uart_port *port, struct serial_struct *ser)
> +{
> +        int ret = 0;
> +        if (ser->type != PORT_UNKNOWN && ser->type != PORT_DCC_JTAG1)
> +                ret = -EINVAL;
> +        if (ser->irq < 0 || ser->irq >= NR_IRQS)
> +                ret = -EINVAL;
> +        if (ser->baud_base < 9600)
> +                ret = -EINVAL;
> +	return ret;

Weirdo indentation style strikes again.

> +}
> +
> +static struct uart_ops dcc_pops = {
> +	.tx_empty	= dcc_tx_empty,
> +	.set_mctrl	= dcc_set_mctrl,
> +	.get_mctrl	= dcc_get_mctrl,
> +	.stop_tx	= dcc_stop_tx,
> +	.start_tx	= dcc_start_tx,
> +	.stop_rx	= dcc_stop_rx,
> +	.enable_ms	= dcc_enable_ms,
> +	.break_ctl	= dcc_break_ctl,
> +	.startup	= dcc_startup,
> +	.shutdown	= dcc_shutdown,
> +	.set_termios	= dcc_set_termios,
> +	.type		= dcc_type,
> +	.release_port	= dcc_release_port,
> +	.request_port	= dcc_request_port,
> +	.config_port	= dcc_config_port,
> +	.verify_port	= dcc_verify_port,
> +};
> +
> +static struct uart_port dcc_ports[UART_NR] = {

If there's only one port, this array isn't required.

> +	{
> +		.membase	= (char*)0x12345678,	/* we need these garbages */
> +		.mapbase	= 0x12345678,		/* for serial_core.c */
> +		.iotype		= SERIAL_IO_MEM,	

.iotype should be UPIO_xxx not SERIAL_IO_xxx.

> +#ifdef DCC_IRQ_USED
> +		.irq		= INT_N_EXT0,
> +#else
> +		.irq		= 0,
> +#endif
> +		.uartclk	= 14745600,			 
> +		.fifosize	= 0,
> +		.ops		= &dcc_pops,
> +		.flags		= ASYNC_BOOT_AUTOCONF,

.flags should be UPF_xxx not ASYNC_xxx.

> +		.line		= 0,
> +	},
> +};
> +
> +
> +#ifdef CONFIG_SERIAL_DCC_CONSOLE
> +
> +static void
> +dcc_console_write(struct console *co, const char *s, unsigned int count)
> +{
> +	xmit_string_CR((char*)s, count);
> +}
> +
> +/*
> + * Read the current UART setup.
> + */
> +static void __init
> +dcc_console_get_options(struct uart_port *port, int *baud, int *parity, int 
> *bits)
> +{
> +	*baud = 9600;
> +	*parity = 'n';
> +	*bits = 8;
> +}

Unnecessary function.

> +
> +static int __init
> +dcc_console_setup(struct console *co, char *options)
> +{
> +	struct uart_port *port;
> +	int baud = 9600;
> +	int bits = 8;
> +	int parity = 'n';
> +	int flow = 'n';
> +
> +	if (co->index >= UART_NR)
> +		co->index = 0;
> +	port = &dcc_ports[co->index];

If you're not likely to have more than one port, this doesn't make sense.

> +
> +	if (options)
> +		uart_parse_options(options, &baud, &parity, &bits, &flow);
> +	else
> +		dcc_console_get_options(port, &baud, &parity, &bits);
> +
> +	return uart_set_options(port, co, baud, parity, bits, flow);
> +}
> +
> +extern struct uart_driver dcc_reg;
> +static struct console dcc_console = {
> +	.name		= SERIAL_DCC_NAME,
> +	.write		= dcc_console_write,
> +	.device		= uart_console_device,
> +	.setup		= dcc_console_setup,
> +	.flags		= CON_PRINTBUFFER,
> +	.index		= -1,
> +	.data		= &dcc_reg,
> +};
> +
> +static int __init dcc_console_init(void)
> +{
> +	register_console(&dcc_console);
> +	return 0;
> +}
> +console_initcall(dcc_console_init);
> +
> +#define DCC_CONSOLE		&dcc_console
> +#else
> +#define DCC_CONSOLE		NULL
> +#endif
> +
> +static struct uart_driver dcc_reg = {
> +	.owner			= THIS_MODULE,
> +	.driver_name		= SERIAL_DCC_NAME,
> +	.dev_name		= SERIAL_DCC_NAME,
> +	.major			= SERIAL_DCC_MAJOR,
> +	.minor			= SERIAL_DCC_MINOR,
> +	.nr			= UART_NR,
> +	.cons			= DCC_CONSOLE,
> +};
> +
> +static int __init
> +dcc_init(void)
> +{
> +	int i, ret = 0;
> +
> +	printk(KERN_INFO "DCC: JTAG1 Serial emulation driver driver $Revision: 1.1 
> $\n");
> +
> +	ret = uart_register_driver(&dcc_reg);
> +
> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < UART_NR; i++)
> +		uart_add_one_port(&dcc_reg, &dcc_ports[i]);

Are you likely to have more than one port?  Does this loop really make
sense?

> +
> +	return ret;
> +}
> +
> +__initcall(dcc_init);
> +
> +MODULE_DESCRIPTION("DCC(JTAG1) JTAG debugger console emulation driver");
> +MODULE_AUTHOR("Hyok S. Choi <hyok.choi@xxxxxxxxxxx>");
> +MODULE_SUPPORTED_DEVICE("ttyJ");
> +MODULE_LICENSE("GPL");

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/