[PATCH 2/4] serial: 8250: Implement wakeup for TX and use it for 8250_omap

Tony Lindgren
2021-09-30T06:29:22Z

We can use the wakeup() and uart_start_pending_tx() calls to wake up an
idle serial port and send out the pending TX buffer on runtime PM resume.
This allows us to remove the depedency to pm_runtime_irq_safe() for
8250_omap driver in the following patches.

We manage the port runtime_suspended flag in the serial port driver as
only the driver knows when the hardware is runtime PM suspended. Note that
The current flag for rpm_tx_active cannot be used as it is TX specific
for 8250_port.

We already have serial8250_start_tx() call serial8250_rpm_get_tx(), and
serial8250_stop_tx() call serial8250_rpm_put_tx() to take care of the
runtime PM usage count for TX. To have the serial port driver call
uart_start_pending_tx() on runtime resume, we must now use just
pm_runtime_get() for serial8250_start_tx() instead of the sync version.

With these changes we must now also flip 8250_omap driver over to call
uart_start_pending_tx(). That's currently the only user of UART_CAP_RPM.

Signed-off-by: Tony Lindgren <tony@atomide.com>
---
drivers/tty/serial/8250/8250_omap.c | 12 ++++++++++
drivers/tty/serial/8250/8250_port.c | 35 ++++++++++++++++++++++++++++-
2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -1593,12 +1593,15 @@ static int omap8250_runtime_suspend(struct device *dev)
{
struct omap8250_priv *priv = dev_get_drvdata(dev);
struct uart_8250_port *up;
+ struct uart_port *port;

/* In case runtime-pm tries this before we are setup */
if (!priv)
return 0;

up = serial8250_get_port(priv->line);
+ port = &up->port;
+
/*
* When using 'no_console_suspend', the console UART must not be
* suspended. Since driver suspend is managed by runtime suspend,
@@ -1610,6 +1613,8 @@ static int omap8250_runtime_suspend(struct device *dev)
return -EBUSY;
}

+ atomic_set(&port->runtime_suspended, 1);
+
if (priv->habit & UART_ERRATA_CLOCK_DISABLE) {
int ret;

@@ -1636,12 +1641,14 @@ static int omap8250_runtime_resume(struct device *dev)
{
struct omap8250_priv *priv = dev_get_drvdata(dev);
struct uart_8250_port *up;
+ struct uart_port *port;

/* In case runtime-pm tries this before we are setup */
if (!priv)
return 0;

up = serial8250_get_port(priv->line);
+ port = &up->port;

if (omap8250_lost_context(up))
omap8250_restore_regs(up);
@@ -1651,6 +1658,11 @@ static int omap8250_runtime_resume(struct device *dev)

priv->latency = priv->calc_latency;
schedule_work(&priv->qos_work);
+
+ atomic_set(&port->runtime_suspended, 0);
+
+ uart_start_pending_tx(port);
+
return 0;
}
#endif
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -724,7 +724,7 @@ void serial8250_rpm_get_tx(struct uart_8250_port *p)
rpm_active = xchg(&p->rpm_tx_active, 1);
if (rpm_active)
return;
- pm_runtime_get_sync(p->port.dev);
+ pm_runtime_get(p->port.dev);
}
EXPORT_SYMBOL_GPL(serial8250_rpm_get_tx);

@@ -2507,6 +2507,38 @@ static void serial8250_shutdown(struct uart_port *port)
serial8250_do_shutdown(port);
}

+/*
+ * Wakes up the serial port if it has been runtime PM suspended.
+ *
+ * Note that we rely on the serial8250_rpm functions to manage the
+ * runtime PM usage count. We also currently depend on the runtime
+ * PM autosuspend timeout to keep the port awake until start_tx().
+ * Eventually we should just use runtime PM functions and not rely
+ * on the autosuspend timeout.
+ */
+static int serial8250_wakeup(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+ struct device *dev = up->port.dev;
+ int err;
+
+ if (!(up->capabilities & UART_CAP_RPM))
+ return 0;
+
+ if (!atomic_read(&port->runtime_suspended)) {
+ pm_runtime_mark_last_busy(dev);
+ return 0;
+ }
+
+ err = pm_request_resume(dev);
+ if (err < 0) {
+ dev_warn(dev, "wakeup failed: %d\n", err);
+ return err;
+ }
+
+ return -EINPROGRESS;
+}
+
/* Nuvoton NPCM UARTs have a custom divisor calculation */
static unsigned int npcm_get_divisor(struct uart_8250_port *up,
unsigned int baud)
@@ -3235,6 +3267,7 @@ static const struct uart_ops serial8250_pops = {
.break_ctl = serial8250_break_ctl,
.startup = serial8250_startup,
.shutdown = serial8250_shutdown,
+ .wakeup = serial8250_wakeup,
.set_termios = serial8250_set_termios,
.set_ldisc = serial8250_set_ldisc,
.pm = serial8250_pm,
--
2.33.0