[PATCH v3 13/14] serial: liteuart: add IRQ support for the TX path

Gabriel Somlo
2022-11-12T21:22:32Z

Modify the TX path to operate in an IRQ-compatible way, while
maintaining support for polling mode via the poll timer.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
---
drivers/tty/serial/liteuart.c | 67 ++++++++++++++++++++++++-----------
1 file changed, 47 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
index e30adb30277f..307c27398e30 100644
--- a/drivers/tty/serial/liteuart.c
+++ b/drivers/tty/serial/liteuart.c
@@ -46,6 +46,7 @@ struct liteuart_port {
struct uart_port port;
struct timer_list timer;
u32 id;
+ bool poll_tx_started;
};

#define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
@@ -78,29 +79,24 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)

static void liteuart_stop_tx(struct uart_port *port)
{
- /* not used in LiteUART, but called unconditionally from serial_core */
+ if (port->irq) {
+ u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
+ litex_write8(port->membase + OFF_EV_ENABLE, irq_mask & ~EV_TX);
+ } else {
+ struct liteuart_port *uart = to_liteuart_port(port);
+ uart->poll_tx_started = false;
+ }
}

static void liteuart_start_tx(struct uart_port *port)
{
- struct circ_buf *xmit = &port->state->xmit;
- unsigned char ch;
-
- if (unlikely(port->x_char)) {
- litex_write8(port->membase + OFF_RXTX, port->x_char);
- port->icount.tx++;
- port->x_char = 0;
- } else if (!uart_circ_empty(xmit)) {
- while (xmit->head != xmit->tail) {
- ch = xmit->buf[xmit->tail];
- xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
- port->icount.tx++;
- liteuart_putchar(port, ch);
- }
+ if (port->irq) {
+ u8 irq_mask = litex_read8(port->membase + OFF_EV_ENABLE);
+ litex_write8(port->membase + OFF_EV_ENABLE, irq_mask | EV_TX);
+ } else {
+ struct liteuart_port *uart = to_liteuart_port(port);
+ uart->poll_tx_started = true;
}
-
- if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
- uart_write_wakeup(port);
}

static void liteuart_stop_rx(struct uart_port *port)
@@ -131,18 +127,47 @@ static void liteuart_rx_chars(struct uart_port *port)
tty_flip_buffer_push(&port->state->port);
}

+static void liteuart_tx_chars(struct uart_port *port)
+{
+ struct circ_buf *xmit = &port->state->xmit;
+
+ if (unlikely(port->x_char)) {
+ litex_write8(port->membase + OFF_RXTX, port->x_char);
+ port->x_char = 0;
+ port->icount.tx++;
+ return;
+ }
+
+ while (!litex_read8(port->membase + OFF_TXFULL)) {
+ if (xmit->head == xmit->tail)
+ break;
+ litex_write8(port->membase + OFF_RXTX, xmit->buf[xmit->tail]);
+ xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+ port->icount.tx++;
+ }
+
+ if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+ uart_write_wakeup(port);
+
+ if (uart_circ_empty(xmit))
+ liteuart_stop_tx(port);
+}
+
static irqreturn_t liteuart_interrupt(int irq, void *data)
{
struct liteuart_port *uart = data;
struct uart_port *port = &uart->port;
u8 isr = litex_read8(port->membase + OFF_EV_PENDING);

- /* for now, only rx path triggers interrupts */
- isr &= EV_RX;
+ if (!(port->irq || uart->poll_tx_started))
+ isr &= ~EV_TX; /* polling mode with tx stopped */

spin_lock(&port->lock);
if (isr & EV_RX)
liteuart_rx_chars(port);
+ if (isr & EV_TX) {
+ liteuart_tx_chars(port);
+ }
spin_unlock(&port->lock);

return IRQ_RETVAL(isr);
@@ -196,6 +221,7 @@ static int liteuart_startup(struct uart_port *port)
}

if (!port->irq) {
+ uart->poll_tx_started = false;
timer_setup(&uart->timer, liteuart_timer, 0);
mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
}
@@ -210,6 +236,7 @@ static void liteuart_shutdown(struct uart_port *port)
struct liteuart_port *uart = to_liteuart_port(port);

litex_write8(port->membase + OFF_EV_ENABLE, 0);
+ uart->poll_tx_started = false;

if (port->irq)
free_irq(port->irq, port);
--
2.37.3