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Message-ID: <YaX/L6n0vzrjLaoF@hovoldconsulting.com>
Date: Tue, 30 Nov 2021 11:38:39 +0100
From: Johan Hovold <johan@...nel.org>
To: Tony Lindgren <tony@...mide.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@...el.com>,
Jiri Slaby <jirislaby@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Vignesh Raghavendra <vigneshr@...com>,
linux-serial@...r.kernel.org, linux-omap@...r.kernel.org,
linux-kernel@...r.kernel.org,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 4/7] serial: 8250: Implement wakeup for TX and use it for
8250_omap
On Mon, Nov 15, 2021 at 10:42:00AM +0200, Tony Lindgren wrote:
> 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 dependency 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 the 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@...mide.com>
> ---
> drivers/tty/serial/8250/8250_omap.c | 19 ++++++++++++++
> drivers/tty/serial/8250/8250_port.c | 39 ++++++++++++++++++++++++++++-
> 2 files changed, 57 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 +1593,16 @@ 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;
> + unsigned long flags;
>
> /* 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 +1614,10 @@ static int omap8250_runtime_suspend(struct device *dev)
> return -EBUSY;
> }
>
> + spin_lock_irqsave(&port->lock, flags);
> + port->runtime_suspended = 1;
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> if (priv->habit & UART_ERRATA_CLOCK_DISABLE) {
> int ret;
>
> @@ -1636,13 +1644,18 @@ 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;
> + unsigned long flags;
>
> /* In case runtime-pm tries this before we are setup */
> if (!priv)
> return 0;
>
> up = serial8250_get_port(priv->line);
> + port = &up->port;
>
> + /* Restore state with interrupts disabled */
> + spin_lock_irqsave(&port->lock, flags);
> if (omap8250_lost_context(up))
> omap8250_restore_regs(up);
>
> @@ -1651,6 +1664,12 @@ static int omap8250_runtime_resume(struct device *dev)
>
> priv->latency = priv->calc_latency;
> schedule_work(&priv->qos_work);
> +
> + port->runtime_suspended = 0;
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> + 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);
>
> @@ -2509,6 +2509,42 @@ 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.
> + *
> + * Caller must hold port->lock for port->runtime_suspended status.
> + * Also the port drivers must hold port->lock when changing the
> + * state for port->runtime_suspended in runtime PM functions.
> + */
> +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 (!pm_runtime_enabled(dev))
> + return 0;
> +
> + if (!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;
> +}
Why can't this be done in core?
> +
> /* Nuvoton NPCM UARTs have a custom divisor calculation */
> static unsigned int npcm_get_divisor(struct uart_8250_port *up,
> unsigned int baud)
> @@ -3237,6 +3273,7 @@ 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,
Johan
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