* [PATCH v2 1/2] serial: 8250: Add dts binding to rate limit serial port during overruns
@ 2018-12-05 0:50 Darwin Dingel
2018-12-05 0:50 ` [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns Darwin Dingel
0 siblings, 1 reply; 3+ messages in thread
From: Darwin Dingel @ 2018-12-05 0:50 UTC (permalink / raw)
To: andriy.shevchenko, gregkh, jslaby, linux-serial
Cc: linux-kernel, Darwin Dingel
When this dts binding is enabled and input overrun on the serial port is
detected, serial port receive will be throttled to give some breathing room
for processing other tasks. This is particularly useful to avoid situations
where serial port HW malfunctions triggering input overruns and then other
processes get starved of processing time. Value provided will be in
milliseconds.
&serial0{
overrun-throttle-ms = <500>;
};
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jiri Slaby <jslaby@suse.com>
Signed-off-by: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz>
---
Documentation/devicetree/bindings/serial/8250.txt | 1 +
1 file changed, 1 insertion(+)
diff --git a/Documentation/devicetree/bindings/serial/8250.txt b/Documentation/devicetree/bindings/serial/8250.txt
index aeb6db4e35c3..da50321da34d 100644
--- a/Documentation/devicetree/bindings/serial/8250.txt
+++ b/Documentation/devicetree/bindings/serial/8250.txt
@@ -51,6 +51,7 @@ Optional properties:
- tx-threshold: Specify the TX FIFO low water indication for parts with
programmable TX FIFO thresholds.
- resets : phandle + reset specifier pairs
+- overrun-throttle-ms : how long to pause uart rx when input overrun is encountered.
Note:
* fsl,ns16550:
--
2.19.2
changes in v2:
- separated dts binding to another patch
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns 2018-12-05 0:50 [PATCH v2 1/2] serial: 8250: Add dts binding to rate limit serial port during overruns Darwin Dingel @ 2018-12-05 0:50 ` Darwin Dingel 2018-12-05 1:41 ` Darwin Dingel 0 siblings, 1 reply; 3+ messages in thread From: Darwin Dingel @ 2018-12-05 0:50 UTC (permalink / raw) To: andriy.shevchenko, gregkh, jslaby, linux-serial Cc: linux-kernel, Darwin Dingel When a serial port gets faulty or gets flooded with inputs, its interrupt handler starts to work double time to get the characters to the workqueue for the tty layer to handle them. When this busy time on the serial/tty subsystem happens during boot, where it is also busy on the userspace trying to initialise, some processes can continuously get preempted and will be on hold until the interrupts subside. The fix is to backoff on processing received characters for a specified amount of time when an input overrun is seen (received a new character before the previous one is processed). This only stops receive and will continue to transmit characters to serial port. After the backoff period is done, it receive will be re-enabled. This is optional and will only be enabled by setting 'overrun-throttle-ms' in the dts. Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Jiri Slaby <jslaby@suse.com> Signed-off-by: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz> --- drivers/tty/serial/8250/8250_core.c | 25 +++++++++++++++++++++++++ drivers/tty/serial/8250/8250_fsl.c | 23 ++++++++++++++++++++++- drivers/tty/serial/8250/8250_of.c | 5 +++++ include/linux/serial_8250.h | 4 ++++ 4 files changed, 56 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 94f3e1c64490..189ab1212d9a 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -942,6 +942,21 @@ static struct uart_8250_port *serial8250_find_match_or_unused(struct uart_port * return NULL; } +static void serial_8250_overrun_backoff_work(struct work_struct *work) +{ + struct uart_8250_port *up = + container_of(to_delayed_work(work), struct uart_8250_port, + overrun_backoff); + struct uart_port *port = &up->port; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + up->ier |= UART_IER_RLSI | UART_IER_RDI; + up->port.read_status_mask |= UART_LSR_DR; + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&port->lock, flags); +} + /** * serial8250_register_8250_port - register a serial port * @up: serial port template @@ -1056,6 +1071,16 @@ int serial8250_register_8250_port(struct uart_8250_port *up) ret = 0; } } + + /* Initialise interrupt backoff work if required */ + if (up->overrun_backoff_time_ms > 0) { + uart->overrun_backoff_time_ms = up->overrun_backoff_time_ms; + INIT_DELAYED_WORK(&uart->overrun_backoff, + serial_8250_overrun_backoff_work); + } else { + uart->overrun_backoff_time_ms = 0; + } + mutex_unlock(&serial_mutex); return ret; diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 6640a4c7ddd1..bb9571eed275 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -45,8 +45,29 @@ int fsl8250_handle_irq(struct uart_port *port) lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR); - if (lsr & (UART_LSR_DR | UART_LSR_BI)) + /* Process incoming characters first */ + if ((lsr & (UART_LSR_DR | UART_LSR_BI)) && + (up->ier & (UART_IER_RLSI | UART_IER_RDI))) { lsr = serial8250_rx_chars(up, lsr); + } + + /* Stop processing interrupts on input overrun */ + if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) { + unsigned long delay; + + up->ier = port->serial_in(port, UART_IER); + if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) { + port->ops->stop_rx(port); + } else { + /* Keep restarting the timer until + * the input overrun subsides. + */ + cancel_delayed_work(&up->overrun_backoff); + } + + delay = msecs_to_jiffies(up->overrun_backoff_time_ms); + schedule_delayed_work(&up->overrun_backoff, delay); + } serial8250_modem_status(up); diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c index 877fd7f8a8ed..a1a85805d010 100644 --- a/drivers/tty/serial/8250/8250_of.c +++ b/drivers/tty/serial/8250/8250_of.c @@ -240,6 +240,11 @@ static int of_platform_serial_probe(struct platform_device *ofdev) if (of_property_read_bool(ofdev->dev.of_node, "auto-flow-control")) port8250.capabilities |= UART_CAP_AFE; + if (of_property_read_u32(ofdev->dev.of_node, + "overrun-throttle-ms", + &port8250.overrun_backoff_time_ms) != 0) + port8250.overrun_backoff_time_ms = 0; + ret = serial8250_register_8250_port(&port8250); if (ret < 0) goto err_dispose; diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 18e21427bce4..5a655ba8d273 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -134,6 +134,10 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + + /* Serial port overrun backoff */ + struct delayed_work overrun_backoff; + u32 overrun_backoff_time_ms; }; static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up) -- 2.19.2 changes in v2: - separated dts binding to another patch ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns 2018-12-05 0:50 ` [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns Darwin Dingel @ 2018-12-05 1:41 ` Darwin Dingel 0 siblings, 0 replies; 3+ messages in thread From: Darwin Dingel @ 2018-12-05 1:41 UTC (permalink / raw) To: andriy.shevchenko, gregkh, jslaby, linux-serial; +Cc: linux-kernel So sorry for the premature "Reviewed-by" bits on the commit messages on the previous patches submitted. Please ignore these while I fix the patch up for v3. Regards, Darwin ________________________________________ From: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz> Sent: Wednesday, 5 December 2018 1:50 p.m. To: andriy.shevchenko@linux.intel.com; gregkh@linuxfoundation.org; jslaby@suse.com; linux-serial@vger.kernel.org Cc: linux-kernel@vger.kernel.org; Darwin Dingel Subject: [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns When a serial port gets faulty or gets flooded with inputs, its interrupt handler starts to work double time to get the characters to the workqueue for the tty layer to handle them. When this busy time on the serial/tty subsystem happens during boot, where it is also busy on the userspace trying to initialise, some processes can continuously get preempted and will be on hold until the interrupts subside. The fix is to backoff on processing received characters for a specified amount of time when an input overrun is seen (received a new character before the previous one is processed). This only stops receive and will continue to transmit characters to serial port. After the backoff period is done, it receive will be re-enabled. This is optional and will only be enabled by setting 'overrun-throttle-ms' in the dts. Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Jiri Slaby <jslaby@suse.com> Signed-off-by: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz> --- drivers/tty/serial/8250/8250_core.c | 25 +++++++++++++++++++++++++ drivers/tty/serial/8250/8250_fsl.c | 23 ++++++++++++++++++++++- drivers/tty/serial/8250/8250_of.c | 5 +++++ include/linux/serial_8250.h | 4 ++++ 4 files changed, 56 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 94f3e1c64490..189ab1212d9a 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -942,6 +942,21 @@ static struct uart_8250_port *serial8250_find_match_or_unused(struct uart_port * return NULL; } +static void serial_8250_overrun_backoff_work(struct work_struct *work) +{ + struct uart_8250_port *up = + container_of(to_delayed_work(work), struct uart_8250_port, + overrun_backoff); + struct uart_port *port = &up->port; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + up->ier |= UART_IER_RLSI | UART_IER_RDI; + up->port.read_status_mask |= UART_LSR_DR; + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&port->lock, flags); +} + /** * serial8250_register_8250_port - register a serial port * @up: serial port template @@ -1056,6 +1071,16 @@ int serial8250_register_8250_port(struct uart_8250_port *up) ret = 0; } } + + /* Initialise interrupt backoff work if required */ + if (up->overrun_backoff_time_ms > 0) { + uart->overrun_backoff_time_ms = up->overrun_backoff_time_ms; + INIT_DELAYED_WORK(&uart->overrun_backoff, + serial_8250_overrun_backoff_work); + } else { + uart->overrun_backoff_time_ms = 0; + } + mutex_unlock(&serial_mutex); return ret; diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 6640a4c7ddd1..bb9571eed275 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -45,8 +45,29 @@ int fsl8250_handle_irq(struct uart_port *port) lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR); - if (lsr & (UART_LSR_DR | UART_LSR_BI)) + /* Process incoming characters first */ + if ((lsr & (UART_LSR_DR | UART_LSR_BI)) && + (up->ier & (UART_IER_RLSI | UART_IER_RDI))) { lsr = serial8250_rx_chars(up, lsr); + } + + /* Stop processing interrupts on input overrun */ + if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) { + unsigned long delay; + + up->ier = port->serial_in(port, UART_IER); + if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) { + port->ops->stop_rx(port); + } else { + /* Keep restarting the timer until + * the input overrun subsides. + */ + cancel_delayed_work(&up->overrun_backoff); + } + + delay = msecs_to_jiffies(up->overrun_backoff_time_ms); + schedule_delayed_work(&up->overrun_backoff, delay); + } serial8250_modem_status(up); diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c index 877fd7f8a8ed..a1a85805d010 100644 --- a/drivers/tty/serial/8250/8250_of.c +++ b/drivers/tty/serial/8250/8250_of.c @@ -240,6 +240,11 @@ static int of_platform_serial_probe(struct platform_device *ofdev) if (of_property_read_bool(ofdev->dev.of_node, "auto-flow-control")) port8250.capabilities |= UART_CAP_AFE; + if (of_property_read_u32(ofdev->dev.of_node, + "overrun-throttle-ms", + &port8250.overrun_backoff_time_ms) != 0) + port8250.overrun_backoff_time_ms = 0; + ret = serial8250_register_8250_port(&port8250); if (ret < 0) goto err_dispose; diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 18e21427bce4..5a655ba8d273 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -134,6 +134,10 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + + /* Serial port overrun backoff */ + struct delayed_work overrun_backoff; + u32 overrun_backoff_time_ms; }; static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up) -- 2.19.2 changes in v2: - separated dts binding to another patch ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2018-12-05 1:42 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-12-05 0:50 [PATCH v2 1/2] serial: 8250: Add dts binding to rate limit serial port during overruns Darwin Dingel 2018-12-05 0:50 ` [PATCH v2 2/2] serial: 8250: Rate limit serial port rx interrupts during input overruns Darwin Dingel 2018-12-05 1:41 ` Darwin Dingel
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