| Message ID | 20211115084203.56478-3-tony@atomide.com |
|---|---|
| State | New |
| Headers | show |
| Series | Serial port generic PM to fix 8250 PM | expand |
On Mon, Nov 15, 2021 at 10:41:58AM +0200, Tony Lindgren wrote: > If the serial driver implements PM runtime with autosuspend, the port may > be powered down on TX. To wake up the port, let's add new wakeup() call > for serial drivers to implement as needed. We can call wakeup() from > __uart_start() before attempting to write to the serial port registers. This needs more detail on the approach taken to handle tx and the issues involved (e.g. stalled ports etc). > Let's keep track of the serial port with a new runtime_suspended flag > that the device driver runtime PM suspend and resume can manage with > port->lock held. This is because only the device driver knows what the > device runtime PM state as in Documentation/power/runtime_pm.rst > under "9. Autosuspend, or automatically-delayed suspend" for locking. > > To allow the serial port drivers to send out pending tx on runtime PM > resume, let's add start_pending_tx() as suggested by Johan Hovold > <johan@kernel.org>. > > Suggested-by: Johan Hovold <johan@kernel.org> > Signed-off-by: Tony Lindgren <tony@atomide.com> > --- > Documentation/driver-api/serial/driver.rst | 9 ++++ > drivers/tty/serial/serial_core.c | 49 +++++++++++++++++++++- > include/linux/serial_core.h | 3 ++ > 3 files changed, 59 insertions(+), 2 deletions(-) > > diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst > --- a/Documentation/driver-api/serial/driver.rst > +++ b/Documentation/driver-api/serial/driver.rst > @@ -234,6 +234,15 @@ hardware. > > Interrupts: caller dependent. > > + wakeup(port) > + Wake up port if it has been runtime PM suspended. > + > + Locking: port->lock taken. > + > + Interrupts: locally disabled. > + > + This call must not sleep > + > flush_buffer(port) > Flush any write buffers, reset any DMA state and stop any > ongoing DMA transfers. > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -107,12 +107,35 @@ static int serial_pm_resume_and_get(struct device *dev) > return pm_runtime_resume_and_get(dev); > } > > +/* Only increments the runtime PM usage count */ > +static void serial_pm_get_noresume(struct device *dev) > +{ > + pm_runtime_get_noresume(dev); > +} > + > static void serial_pm_autosuspend(struct device *dev) > { > pm_runtime_mark_last_busy(dev); > pm_runtime_put_autosuspend(dev); > } > > +/* > + * This routine can be used before register access to wake up a serial > + * port that has been runtime PM suspended by the serial port driver. > + * Note that the runtime_suspended flag is managed by the serial port > + * device driver runtime PM. > + */ > +static int __uart_port_wakeup(struct uart_port *port) > +{ > + if (!port->runtime_suspended) > + return 0; > + > + if (port->ops->wakeup) > + return port->ops->wakeup(port); Why do you need a subdriver callback for this? Why no schedule a resume in core rather than spreading the logic out over core and subdrivers? > + > + return 0; > +} > + > /* > * This routine is used by the interrupt handler to schedule processing in > * the software interrupt portion of the driver. > @@ -145,8 +168,15 @@ static void __uart_start(struct tty_struct *tty) > struct uart_state *state = tty->driver_data; > struct uart_port *port = state->uart_port; > > - if (port && !uart_tx_stopped(port)) > - port->ops->start_tx(port); > + if (!port || uart_tx_stopped(port)) > + return; > + > + if (__uart_port_wakeup(port) < 0) > + return; > + This is racy since nothing prevents the device from being suspended right here. > + serial_pm_get_noresume(port->dev); > + port->ops->start_tx(port); > + serial_pm_autosuspend(port->dev); > } > > static void uart_start(struct tty_struct *tty) > @@ -160,6 +190,21 @@ static void uart_start(struct tty_struct *tty) > uart_port_unlock(port, flags); > } > > +/* > + * This routine can be called from the serial driver runtime PM resume function > + * to transmit buffered data if the serial port was not active on uart_write(). > + */ > +void uart_start_pending_tx(struct uart_port *port) > +{ > + unsigned long flags; > + > + spin_lock_irqsave(&port->lock, flags); > + if (!uart_tx_stopped(port) && uart_circ_chars_pending(&port->state->xmit)) > + port->ops->start_tx(port); > + spin_unlock_irqrestore(&port->lock, flags); > +} > +EXPORT_SYMBOL(uart_start_pending_tx); Perhaps as an intermediate step, but this looks like another argument for handling everything runtime PM related in core (i.e. enabling runtime pm and generic suspend/resume ops) and adding callbacks to do subdriver specific bits instead. > + > static void > uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear) > { > diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h > --- a/include/linux/serial_core.h > +++ b/include/linux/serial_core.h > @@ -40,6 +40,7 @@ struct uart_ops { > void (*set_mctrl)(struct uart_port *, unsigned int mctrl); > unsigned int (*get_mctrl)(struct uart_port *); > void (*stop_tx)(struct uart_port *); > + int (*wakeup)(struct uart_port *); > void (*start_tx)(struct uart_port *); > void (*throttle)(struct uart_port *); > void (*unthrottle)(struct uart_port *); > @@ -250,6 +251,7 @@ struct uart_port { > unsigned char suspended; > unsigned char console_reinit; > const char *name; /* port name */ > + unsigned int runtime_suspended:1; /* port runtime state set by port driver */ > struct attribute_group *attr_group; /* port specific attributes */ > const struct attribute_group **tty_groups; /* all attributes (serial core use only) */ > struct serial_rs485 rs485; > @@ -414,6 +416,7 @@ bool uart_match_port(const struct uart_port *port1, > /* > * Power Management > */ > +void uart_start_pending_tx(struct uart_port *port); > int uart_suspend_port(struct uart_driver *reg, struct uart_port *port); > int uart_resume_port(struct uart_driver *reg, struct uart_port *port); Johan
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst --- a/Documentation/driver-api/serial/driver.rst +++ b/Documentation/driver-api/serial/driver.rst @@ -234,6 +234,15 @@ hardware. Interrupts: caller dependent. + wakeup(port) + Wake up port if it has been runtime PM suspended. + + Locking: port->lock taken. + + Interrupts: locally disabled. + + This call must not sleep + flush_buffer(port) Flush any write buffers, reset any DMA state and stop any ongoing DMA transfers. diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -107,12 +107,35 @@ static int serial_pm_resume_and_get(struct device *dev) return pm_runtime_resume_and_get(dev); } +/* Only increments the runtime PM usage count */ +static void serial_pm_get_noresume(struct device *dev) +{ + pm_runtime_get_noresume(dev); +} + static void serial_pm_autosuspend(struct device *dev) { pm_runtime_mark_last_busy(dev); pm_runtime_put_autosuspend(dev); } +/* + * This routine can be used before register access to wake up a serial + * port that has been runtime PM suspended by the serial port driver. + * Note that the runtime_suspended flag is managed by the serial port + * device driver runtime PM. + */ +static int __uart_port_wakeup(struct uart_port *port) +{ + if (!port->runtime_suspended) + return 0; + + if (port->ops->wakeup) + return port->ops->wakeup(port); + + return 0; +} + /* * This routine is used by the interrupt handler to schedule processing in * the software interrupt portion of the driver. @@ -145,8 +168,15 @@ static void __uart_start(struct tty_struct *tty) struct uart_state *state = tty->driver_data; struct uart_port *port = state->uart_port; - if (port && !uart_tx_stopped(port)) - port->ops->start_tx(port); + if (!port || uart_tx_stopped(port)) + return; + + if (__uart_port_wakeup(port) < 0) + return; + + serial_pm_get_noresume(port->dev); + port->ops->start_tx(port); + serial_pm_autosuspend(port->dev); } static void uart_start(struct tty_struct *tty) @@ -160,6 +190,21 @@ static void uart_start(struct tty_struct *tty) uart_port_unlock(port, flags); } +/* + * This routine can be called from the serial driver runtime PM resume function + * to transmit buffered data if the serial port was not active on uart_write(). + */ +void uart_start_pending_tx(struct uart_port *port) +{ + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + if (!uart_tx_stopped(port) && uart_circ_chars_pending(&port->state->xmit)) + port->ops->start_tx(port); + spin_unlock_irqrestore(&port->lock, flags); +} +EXPORT_SYMBOL(uart_start_pending_tx); + static void uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear) { diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -40,6 +40,7 @@ struct uart_ops { void (*set_mctrl)(struct uart_port *, unsigned int mctrl); unsigned int (*get_mctrl)(struct uart_port *); void (*stop_tx)(struct uart_port *); + int (*wakeup)(struct uart_port *); void (*start_tx)(struct uart_port *); void (*throttle)(struct uart_port *); void (*unthrottle)(struct uart_port *); @@ -250,6 +251,7 @@ struct uart_port { unsigned char suspended; unsigned char console_reinit; const char *name; /* port name */ + unsigned int runtime_suspended:1; /* port runtime state set by port driver */ struct attribute_group *attr_group; /* port specific attributes */ const struct attribute_group **tty_groups; /* all attributes (serial core use only) */ struct serial_rs485 rs485; @@ -414,6 +416,7 @@ bool uart_match_port(const struct uart_port *port1, /* * Power Management */ +void uart_start_pending_tx(struct uart_port *port); int uart_suspend_port(struct uart_driver *reg, struct uart_port *port); int uart_resume_port(struct uart_driver *reg, struct uart_port *port);
If the serial driver implements PM runtime with autosuspend, the port may be powered down on TX. To wake up the port, let's add new wakeup() call for serial drivers to implement as needed. We can call wakeup() from __uart_start() before attempting to write to the serial port registers. Let's keep track of the serial port with a new runtime_suspended flag that the device driver runtime PM suspend and resume can manage with port->lock held. This is because only the device driver knows what the device runtime PM state as in Documentation/power/runtime_pm.rst under "9. Autosuspend, or automatically-delayed suspend" for locking. To allow the serial port drivers to send out pending tx on runtime PM resume, let's add start_pending_tx() as suggested by Johan Hovold <johan@kernel.org>. Suggested-by: Johan Hovold <johan@kernel.org> Signed-off-by: Tony Lindgren <tony@atomide.com> --- Documentation/driver-api/serial/driver.rst | 9 ++++ drivers/tty/serial/serial_core.c | 49 +++++++++++++++++++++- include/linux/serial_core.h | 3 ++ 3 files changed, 59 insertions(+), 2 deletions(-)