Message-ID: <20101022135130.617f0ce8@lxorguk.ukuu.org.uk>
Date:	Fri, 22 Oct 2010 13:51:30 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	pghatwork@...il.com
Cc:	par-gunnar.p.hjalmdahl@...ricsson.com,
	linus.walleij@...ricsson.com, linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] mfd: Add UART support for the ST-Ericsson CG2900.


> + * is_chip_flow_off() - Check if chip has set flow off.
> + * @tty:	Pointer to tty.
> + *
> + * Returns:
> + *   true - chip flows off.
> + *   false - chip flows on.
> + */
> +static bool is_chip_flow_off(struct tty_struct *tty)
> +{
> +	int lines;
> +
> +	lines = tty->ops->tiocmget(tty, uart_info->fd);
> +
> +	if (lines & TIOCM_CTS)
> +		return false;
> +	else
> +		return true;
> +}

What if the device doesn't have a tiocmget ? You must check this. If you
want to call into the ttys own tiocmget froma sleeping context fine, but
see tty_tiocmget and you'll notice you need to check the op is non NULL
somewhere. You could do this when the ldisc is opened and refuse to open
- some ldiscs do that


> +
> +/**
> + * create_work_item() - Create work item and add it to the work queue.
> + * @wq:		work queue struct where the work will be added.
> + * @work_func:	Work function.
> + * @data:	Private data for the work.
> + *
> + * Returns:
> + *   0 if there is no error.
> + *   -EBUSY if not possible to queue work.
> + *   -ENOMEM if allocation fails.
> + */
> +static int create_work_item(struct workqueue_struct *wq, work_func_t work_func,
> +			    void *data)
> +{
> +	struct uart_work_struct *new_work;
> +	int err;
> +
> +	new_work = kmalloc(sizeof(*new_work), GFP_ATOMIC);

So instead of a tiny object embedded in your device you've got a whole
error path to worry about, a printk disguised in a macro and a text
string longer than the struct size ? Surely this should be part of the
device

> +	if (!new_work) {
> +		CG2900_ERR("Failed to alloc memory for uart_work_struct!");

Please use the standard dev_dbg etc functionality - or pr_err etc when
you have no device pointer. The newest kernel tty object has a device
pointer added so you could use that.


> + * set_tty_baud() - Called to set specific baud in TTY.
> + * @tty:	Tty device.
> + * @baud:	Baud to set.
> + *
> + * Returns:
> + *   true - baudrate set with success.
> + *   false - baundrate set failure.
> + */
> +static bool set_tty_baud(struct tty_struct *tty, int baud)
> +{
> +	struct ktermios *old_termios;
> +	bool retval = true;
> +
> +	old_termios = kmalloc(sizeof(*old_termios), GFP_ATOMIC);

termios struct is easily small enough to be fine on the stack

> +	/* Let's mark that CG2900 driver uses c_ispeed and c_ospeed fields. */
> +	tty->termios->c_cflag |= BOTHER;

This shouldn't be needed - the tty_encode_baud_rate logic works out of
BOTHER must be set

> +	tty->termios->c_cflag &= ~BOTHER;

And your termios is now potentially invalid


> +	/* Set IRQ on CTS. */
> +	err = request_irq(pf_data->uart.cts_irq,
> +			  cts_interrupt,
> +			  IRQF_TRIGGER_FALLING,
> +			  UART_NAME,
> +			  NULL);

So we now ave terminal tty/ldisc confusion

> +	if (err) {
> +		CG2900_ERR("Could not request CTS IRQ (%d)", err);
> +		goto error;
> +	}
> +
> +#ifdef CONFIG_PM
> +	enable_irq_wake(pf_data->uart.cts_irq);
> +#endif
> +	return 0;
> +
> +error:
> +	if (pf_data->uart.enable_uart)
> +		(void)pf_data->uart.enable_uart();
> +	return err;

> +}
> +
> +/**
> + * unset_cts_irq() - Disable interrupt on CTS.
> + */
> +static void unset_cts_irq(void)

And no ability to support multiple devices

> +	CG2900_DBG("Clear break");
> +	tty->ops->break_ctl(tty, TTY_BREAK_OFF);

What if the tty doesn't have one ?


> +	if (CHIP_AWAKE == uart_info->sleep_state) {
> +		uart_info->tty->ops->break_ctl(uart_info->tty, TTY_BREAK_ON);

Ditto


> +		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
> +		len = tty->ops->write(tty, skb->data, skb->len);

A tty isn't required to have a write function

> +		if ((BAUD_START == uart_info->baud_rate_state) &&
> +		    (is_set_baud_rate_cmd(skb->data))) {
> +			CG2900_INFO("UART set baud rate cmd found.");
> +			SET_BAUD_STATE(BAUD_SENDING);

Do we really need this all in capitals ?



> + * uart_tty_open() - Called when UART line discipline changed to N_HCI.
> + * @tty:	Pointer to associated TTY instance data.
> + *
> + * Returns:
> + *   0 if there is no error.
> + *   Errors from cg2900_register_trans_driver.
> + */
> +static int uart_tty_open(struct tty_struct *tty)
> +{
> +	int err;
> +
> +	CG2900_INFO("uart_tty_open");
> +
> +	/* Set the structure pointers and set the UART receive room */
> +	uart_info->tty = tty;

You must respect the kref handling in the kernel tty code. Take
references by all means but do it properly.


> +static void uart_tty_wakeup(struct tty_struct *tty)
> +{
> +	int err;
> +
> +	CG2900_INFO("uart_tty_wakeup");
> +
> +	/*
> +	 * Clear the TTY_DO_WRITE_WAKEUP bit that is set in
> +	 * work_do_transmit().
> +	 */
> +	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
> +
> +	if (tty != uart_info->tty)
> +		return;

How can this occur - and why check it after you've changed tty->flags ???


> +/**
> + * uart_tty_receive() - Called by TTY low level driver when receive
> data is available.
> + * @tty:	Pointer to TTY instance data
> + * @data:	Pointer to received data
> + * @flags:	Pointer to flags for data
> + * @count:	Count of received data in bytes
> + */
> +static void uart_tty_receive(struct tty_struct *tty, const u8 *data,
> +			     char *flags, int count)
> +{
> +	CG2900_INFO("uart_tty_receive");
> +
> +	if (tty != uart_info->tty)
> +		return;

Again this is nonsense


> +/*
> + * We don't provide read/write/poll interface for user space.
> + */
> +static ssize_t uart_tty_read(struct tty_struct *tty, struct file *file,
> +			     unsigned char __user *buf, size_t nr)
> +{
> +	CG2900_INFO("uart_tty_read");
> +	return 0;
> +}

-EINVAL then

> +
> +static ssize_t uart_tty_write(struct tty_struct *tty, struct file *file,
> +			      const unsigned char *data, size_t count)
> +{
> +	CG2900_INFO("uart_tty_write");
> +	return count;

This is wrong - you can't jusr vanish the data
> +}



This needs some restructuring I think

A line discipline should contain no hardware awareness, that goes in the
actual uart hardware driver. So we shouldn't have magic irq code in this
part of things.

You also need to sort out the tty kref handling in open/close and the
fact you've got magic hardcoded single instance stuff buried i nit.

Finally tty ldiscs don't go buried in the mfd directory, or they'll get
missed during chanegs/updates. The ldisc probably belongs in bluetooth a
and the hardware support in the mfd directory.


So - NAK this for the moment, it needs to be split cleanly into ldisc
(thing which speaks the protocol and eg sees "speed change required" and
acts on it) and device (thing which knows about the hardware).

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