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Subject[PATCH v4 12/14] serial: liteuart: add IRQ support for the RX path
Date
Add support for IRQ-driven RX. Support for the TX path will be added
in a separate commit.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
---

Changes from v3:
- add shadow irq register to support polling mode and avoid reading
hardware mmio irq register to learn which irq flags are enabled
- this also simplifies both liteuart_interrupt() and liteuart_startup()

drivers/tty/serial/liteuart.c | 76 +++++++++++++++++++++++++++++++----
1 file changed, 69 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
index 8a6e176be08e..fad778578986 100644
--- a/drivers/tty/serial/liteuart.c
+++ b/drivers/tty/serial/liteuart.c
@@ -7,6 +7,7 @@

#include <linux/bits.h>
#include <linux/console.h>
+#include <linux/interrupt.h>
#include <linux/litex.h>
#include <linux/module.h>
#include <linux/of.h>
@@ -46,6 +47,7 @@ struct liteuart_port {
struct uart_port port;
struct timer_list timer;
u32 id;
+ u8 irq_reg;
};

#define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
@@ -76,6 +78,19 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)
litex_write8(port->membase + OFF_RXTX, ch);
}

+static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 mask)
+{
+ struct liteuart_port *uart = to_liteuart_port(port);
+
+ if (set)
+ uart->irq_reg |= mask;
+ else
+ uart->irq_reg &= ~mask;
+
+ if (port->irq)
+ litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
+}
+
static void liteuart_stop_tx(struct uart_port *port)
{
}
@@ -129,13 +144,27 @@ static void liteuart_rx_chars(struct uart_port *port)
tty_flip_buffer_push(&port->state->port);
}

+static irqreturn_t liteuart_interrupt(int irq, void *data)
+{
+ struct liteuart_port *uart = data;
+ struct uart_port *port = &uart->port;
+ u8 isr;
+
+ spin_lock(&port->lock);
+ isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
+ if (isr & EV_RX)
+ liteuart_rx_chars(port);
+ spin_unlock(&port->lock);
+
+ return IRQ_RETVAL(isr);
+}
+
static void liteuart_timer(struct timer_list *t)
{
struct liteuart_port *uart = from_timer(uart, t, timer);
struct uart_port *port = &uart->port;

- liteuart_rx_chars(port);
-
+ liteuart_interrupt(0, port);
mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
}

@@ -161,19 +190,45 @@ static unsigned int liteuart_get_mctrl(struct uart_port *port)
static int liteuart_startup(struct uart_port *port)
{
struct liteuart_port *uart = to_liteuart_port(port);
+ unsigned long flags;
+ int ret;

- /* disable events */
- litex_write8(port->membase + OFF_EV_ENABLE, 0);
+ if (port->irq) {
+ ret = request_irq(port->irq, liteuart_interrupt, 0,
+ KBUILD_MODNAME, uart);
+ if (ret) {
+ pr_err(pr_fmt("line %d irq %d failed: using polling\n"),
+ port->line, port->irq);
+ port->irq = 0;
+ }
+ }

- /* prepare timer for polling */
- timer_setup(&uart->timer, liteuart_timer, 0);
- mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+ spin_lock_irqsave(&port->lock, flags);
+ /* only enabling rx irqs during startup */
+ liteuart_update_irq_reg(port, true, EV_RX);
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ if (!port->irq) {
+ timer_setup(&uart->timer, liteuart_timer, 0);
+ mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+ }

return 0;
}

static void liteuart_shutdown(struct uart_port *port)
{
+ struct liteuart_port *uart = to_liteuart_port(port);
+ unsigned long flags;
+
+ spin_lock_irqsave(&port->lock, flags);
+ liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ if (port->irq)
+ free_irq(port->irq, port);
+ else
+ del_timer_sync(&uart->timer);
}

static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
@@ -262,6 +317,13 @@ static int liteuart_probe(struct platform_device *pdev)
goto err_erase_id;
}

+ /* get irq */
+ ret = platform_get_irq_optional(pdev, 0);
+ if (ret < 0 && ret != -ENXIO)
+ return ret;
+ if (ret > 0)
+ port->irq = ret;
+
/* values not from device tree */
port->dev = &pdev->dev;
port->iotype = UPIO_MEM;
--
2.38.1
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