/*
* Custom interrupt handler to manage finer-grained flow control. Although we
* have throttle/unthrottle callbacks, we've seen that the VUART device can
* deliver characters faster than the ldisc has a chance to check buffer space
* against the throttle threshold. This results in dropped characters before
* the throttle.
*
* We do this by checking for flip buffer space before RX. If we have no space,
* throttle now and schedule an unthrottle for later, once the ldisc has had
* a chance to drain the buffers.
*/
static int aspeed_vuart_handle_irq(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
unsigned int iir, lsr;
unsigned long flags;
int space, count;
iir = serial_port_in(port, UART_IIR);
if (iir & UART_IIR_NO_INT)
return 0;
spin_lock_irqsave(&port->lock, flags);
lsr = serial_port_in(port, UART_LSR);
if (lsr & (UART_LSR_DR | UART_LSR_BI)) {
space = tty_buffer_space_avail(&port->state->port);
if (!space) {
/* throttle and schedule an unthrottle later */
struct aspeed_vuart *vuart = port->private_data;
__aspeed_vuart_set_throttle(up, true);
if (!timer_pending(&vuart->unthrottle_timer)) {
vuart->port = up;
mod_timer(&vuart->unthrottle_timer,
jiffies + unthrottle_timeout);
}
} else {
count = min(space, 256);
do {
serial8250_read_char(up, lsr);
lsr = serial_in(up, UART_LSR);
if (--count == 0)
break;
} while (lsr & (UART_LSR_DR | UART_LSR_BI));
tty_flip_buffer_push(&port->state->port);
}
}
serial8250_modem_status(up);
if (lsr & UART_LSR_THRE)
serial8250_tx_chars(up);
spin_unlock_irqrestore(&port->lock, flags);
return 1;
}
static void aspeed_vuart_unthrottle_exp(struct timer_list *timer)
{
struct aspeed_vuart *vuart = from_timer(vuart, timer, unthrottle_timer);
struct uart_8250_port *up = vuart->port;
if (!tty_buffer_space_avail(&up->port.state->port)) {
mod_timer(&vuart->unthrottle_timer,
jiffies + unthrottle_timeout);
return;
}
aspeed_vuart_unthrottle(&up->port);
}
static int pty_space(struct tty_struct *to)
{
int n = tty_buffer_space_avail(to->port);
return min(n, 8192);
}
static int pty_write_room(struct tty_struct *tty)
{
if (tty->stopped)
return 0;
return tty_buffer_space_avail(tty->link->port);
}
