| Message ID | 20211015112626.35359-2-tony@atomide.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Get rid of pm_runtime_irq_safe() for 8250_omap | expand |
On Fri, Oct 15, 2021 at 02:26:23PM +0300, 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() and flow control related functions 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> So this looks somewhat like a step in the right direction, but... > --- > Documentation/driver-api/serial/driver.rst | 9 +++ > drivers/tty/serial/serial_core.c | 68 +++++++++++++++++++++- > include/linux/serial_core.h | 3 + > 3 files changed, 78 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 > @@ -91,6 +91,35 @@ static inline struct uart_port *uart_port_check(struct uart_state *state) > return state->uart_port; > } > > +/* > + * 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; > +} > + > +static int uart_port_wakeup(struct uart_port *port) > +{ > + unsigned long flags; > + int ret; > + > + spin_lock_irqsave(&port->lock, flags); > + ret = __uart_port_wakeup(port); > + spin_unlock_irqrestore(&port->lock, flags); > + > + return ret; > +} > + > /* > * This routine is used by the interrupt handler to schedule processing in > * the software interrupt portion of the driver. > @@ -123,8 +152,13 @@ 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; > + > + port->ops->start_tx(port); > } > > static void uart_start(struct tty_struct *tty) > @@ -138,6 +172,21 @@ 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) > { > @@ -1067,6 +1116,11 @@ uart_tiocmset(struct tty_struct *tty, unsigned int set, unsigned int clear) > if (!uport) > goto out; > > + if (uart_port_wakeup(uport) < 0) { > + ret = -EAGAIN; > + goto out; > + } ...this isn't right. You should just resume the device synchronously here and not return some random error to user space, which it is unlikely to even handle. Now this may require moving more of the runtime PM into serial core, where it should have been added in the first place, due to a lot of the serial callbacks being called with the port spin lock held. The current implementation is just broken. Take uart_dtr_rts(), for example, nothing makes sure that the device is active before accessing the modem control registers there. You're currently just relying on luck and pm_runtime_irq_safe() (which you are now trying to remove). > + > if (!tty_io_error(tty)) { > uart_update_mctrl(uport, set, clear); > ret = 0; > @@ -1402,6 +1456,11 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) > goto out_up; > } > > + if (uart_port_wakeup(uport) < 0) { > + ret = -EAGAIN; > + goto out_up; > + } > + > /* > * All these rely on hardware being present and need to be > * protected against the tty being hung up. > @@ -1724,7 +1783,12 @@ static void uart_dtr_rts(struct tty_port *port, int raise) > uport = uart_port_ref(state); > if (!uport) > return; > + > + if (uart_port_wakeup(uport) < 0) > + goto out; > + > uart_port_dtr_rts(uport, raise); > +out: > uart_port_deref(uport); > } Heh, here you do try to do something about dtr_rts(), but you can't just ignore the request and wish for the best in case the device is suspended. :) There needs to be a synchronous resume here too. Johan
Hi, * Johan Hovold <johan@kernel.org> [211018 07:09]: > On Fri, Oct 15, 2021 at 02:26:23PM +0300, Tony Lindgren wrote: > > @@ -1067,6 +1116,11 @@ uart_tiocmset(struct tty_struct *tty, unsigned int set, unsigned int clear) > > if (!uport) > > goto out; > > > > + if (uart_port_wakeup(uport) < 0) { > > + ret = -EAGAIN; > > + goto out; > > + } > > ...this isn't right. You should just resume the device synchronously > here and not return some random error to user space, which it is > unlikely to even handle. OK I'll check what we can already wake synchronously :) > Now this may require moving more of the runtime PM into serial core, > where it should have been added in the first place, due to a lot of the > serial callbacks being called with the port spin lock held. Yup.. So the good news is that Andy already has the generic serial layer runtime PM changes in his WIP tree. I'll take a look if we can already add some of that without bringing in all the other dependencies. > The current implementation is just broken. Take uart_dtr_rts(), for > example, nothing makes sure that the device is active before accessing > the modem control registers there. You're currently just relying on > luck and pm_runtime_irq_safe() (which you are now trying to remove). Yeah agreed, it's broken. It is usable for at least two limited cases though, which are a serial port console with PM, and bluetooth with PM. The serial port console typically only has RX and TX lines connected, and the bluetooth typically uses out-of-band GPIO pins for wakeups. To enable the serial port PM in general, we need to make sure it is enabled only for applications where it can be used. So it needs to be enabled from the user space as we do for the serial console, or enabled from the consumer device driver for things like bluetooth. Sure the TX should work in all other cases too.. > > + > > + if (uart_port_wakeup(uport) < 0) > > + goto out; > > + > > uart_port_dtr_rts(uport, raise); > > +out: > > uart_port_deref(uport); > > } > > Heh, here you do try to do something about dtr_rts(), but you can't just > ignore the request and wish for the best in case the device is > suspended. :) There needs to be a synchronous resume here too. Well for the current use cases the port should be already awake at this point :) But yeah, for the TX path we should be able to handle all the cases. Regards, Tony
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 @@ -91,6 +91,35 @@ static inline struct uart_port *uart_port_check(struct uart_state *state) return state->uart_port; } +/* + * 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; +} + +static int uart_port_wakeup(struct uart_port *port) +{ + unsigned long flags; + int ret; + + spin_lock_irqsave(&port->lock, flags); + ret = __uart_port_wakeup(port); + spin_unlock_irqrestore(&port->lock, flags); + + return ret; +} + /* * This routine is used by the interrupt handler to schedule processing in * the software interrupt portion of the driver. @@ -123,8 +152,13 @@ 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; + + port->ops->start_tx(port); } static void uart_start(struct tty_struct *tty) @@ -138,6 +172,21 @@ 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) { @@ -1067,6 +1116,11 @@ uart_tiocmset(struct tty_struct *tty, unsigned int set, unsigned int clear) if (!uport) goto out; + if (uart_port_wakeup(uport) < 0) { + ret = -EAGAIN; + goto out; + } + if (!tty_io_error(tty)) { uart_update_mctrl(uport, set, clear); ret = 0; @@ -1402,6 +1456,11 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) goto out_up; } + if (uart_port_wakeup(uport) < 0) { + ret = -EAGAIN; + goto out_up; + } + /* * All these rely on hardware being present and need to be * protected against the tty being hung up. @@ -1724,7 +1783,12 @@ static void uart_dtr_rts(struct tty_port *port, int raise) uport = uart_port_ref(state); if (!uport) return; + + if (uart_port_wakeup(uport) < 0) + goto out; + uart_port_dtr_rts(uport, raise); +out: uart_port_deref(uport); } 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() and flow control related functions 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 | 68 +++++++++++++++++++++- include/linux/serial_core.h | 3 + 3 files changed, 78 insertions(+), 2 deletions(-)