/*
* 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;
}
/*
* This is mostly serial8250_handle_irq(). We have a slightly different DMA
* hoook for RX/TX and need different logic for them in the ISR. Therefore we
* use the default routine in the non-DMA case and this one for with DMA.
*/
static int omap_8250_dma_handle_irq(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
unsigned char status;
unsigned long flags;
u8 iir;
int dma_err = 0;
serial8250_rpm_get(up);
iir = serial_port_in(port, UART_IIR);
if (iir & UART_IIR_NO_INT) {
serial8250_rpm_put(up);
return 0;
}
spin_lock_irqsave(&port->lock, flags);
status = serial_port_in(port, UART_LSR);
if (status & (UART_LSR_DR | UART_LSR_BI)) {
dma_err = omap_8250_rx_dma(up, iir);
if (dma_err) {
status = serial8250_rx_chars(up, status);
omap_8250_rx_dma(up, 0);
}
}
serial8250_modem_status(up);
if (status & UART_LSR_THRE && up->dma->tx_err) {
if (uart_tx_stopped(&up->port) ||
uart_circ_empty(&up->port.state->xmit)) {
up->dma->tx_err = 0;
serial8250_tx_chars(up);
} else {
/*
* try again due to an earlier failer which
* might have been resolved by now.
*/
dma_err = omap_8250_tx_dma(up);
if (dma_err)
serial8250_tx_chars(up);
}
}
spin_unlock_irqrestore(&port->lock, flags);
serial8250_rpm_put(up);
return 1;
}
static irqreturn_t omap8250_irq(int irq, void *dev_id)
{
struct uart_port *port = dev_id;
struct uart_8250_port *up = up_to_u8250p(port);
unsigned int iir;
int ret;
#ifdef CONFIG_SERIAL_8250_DMA
if (up->dma) {
ret = omap_8250_dma_handle_irq(port);
return IRQ_RETVAL(ret);
}
#endif
serial8250_rpm_get(up);
iir = serial_port_in(port, UART_IIR);
ret = serial8250_handle_irq(port, iir);
serial8250_rpm_put(up);
return IRQ_RETVAL(ret);
}
