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Date: Mon, 13 Jun 2022 14:39:05 +0300
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH] serial: Drop timeout from uart_port
Since commit 31f6bd7fad3b ("serial: Store character timing information
to uart_port"), per frame timing information is available on uart_port.
Uart port's timeout can be derived from frame_time by multiplying with
fifosize.
Most callers of uart_poll_timeout are not made under port's lock. To be
on the safe side, make sure frame_time is only accessed once. As
fifo_size is effectively a constant, it shouldn't cause any issues.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
Documentation/driver-api/serial/driver.rst | 5 +++--
drivers/tty/serial/mux.c | 6 ------
drivers/tty/serial/serial_core.c | 25 ++++++++++---------------
include/linux/serial_core.h | 16 ++++++++++++++--
4 files changed, 27 insertions(+), 25 deletions(-)
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst
index 7ef83fd3917b..1e7ab4142d49 100644
--- a/Documentation/driver-api/serial/driver.rst
+++ b/Documentation/driver-api/serial/driver.rst
@@ -422,8 +422,9 @@ Other functions
---------------
uart_update_timeout(port,cflag,baud)
- Update the FIFO drain timeout, port->timeout, according to the
- number of bits, parity, stop bits and baud rate.
+ Update the frame timing information according to the number of bits,
+ parity, stop bits and baud rate. The FIFO drain timeout is derived
+ from the frame timing information.
Locking: caller is expected to take port->lock
diff --git a/drivers/tty/serial/mux.c b/drivers/tty/serial/mux.c
index 643dfbcc43f9..0ba0f4d9459d 100644
--- a/drivers/tty/serial/mux.c
+++ b/drivers/tty/serial/mux.c
@@ -481,12 +481,6 @@ static int __init mux_probe(struct parisc_device *dev)
port->line = port_cnt;
port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_MUX_CONSOLE);
- /* The port->timeout needs to match what is present in
- * uart_wait_until_sent in serial_core.c. Otherwise
- * the time spent in msleep_interruptable will be very
- * long, causing the appearance of a console hang.
- */
- port->timeout = HZ / 50;
spin_lock_init(&port->lock);
status = uart_add_one_port(&mux_driver, port);
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 621fc15e2e54..e068b16d770d 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -327,13 +327,14 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
}
/**
- * uart_update_timeout - update per-port FIFO timeout.
+ * uart_update_timeout - update per-port frame timing information.
* @port: uart_port structure describing the port
* @cflag: termios cflag value
* @baud: speed of the port
*
- * Set the port FIFO timeout value. The @cflag value should
- * reflect the actual hardware settings.
+ * Set the port frame timing information from which the FIFO timeout
+ * value is derived. The @cflag value should reflect the actual hardware
+ * settings.
*/
void
uart_update_timeout(struct uart_port *port, unsigned int cflag,
@@ -343,13 +344,6 @@ uart_update_timeout(struct uart_port *port, unsigned int cflag,
u64 frame_time;
frame_time = (u64)size * NSEC_PER_SEC;
- size *= port->fifosize;
-
- /*
- * Figure the timeout to send the above number of bits.
- * Add .02 seconds of slop
- */
- port->timeout = (HZ * size) / baud + HZ/50;
port->frame_time = DIV64_U64_ROUND_UP(frame_time, baud);
}
EXPORT_SYMBOL(uart_update_timeout);
@@ -1698,7 +1692,7 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
{
struct uart_state *state = tty->driver_data;
struct uart_port *port;
- unsigned long char_time, expire;
+ unsigned long char_time, expire, fifo_timeout;
port = uart_port_ref(state);
if (!port)
@@ -1728,12 +1722,13 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
* amount of time to send the entire FIFO, it probably won't
* ever clear. This assumes the UART isn't doing flow
* control, which is currently the case. Hence, if it ever
- * takes longer than port->timeout, this is probably due to a
+ * takes longer than FIFO timeout, this is probably due to a
* UART bug of some kind. So, we clamp the timeout parameter at
- * 2*port->timeout.
+ * 2 * FIFO timeout.
*/
- if (timeout == 0 || timeout > 2 * port->timeout)
- timeout = 2 * port->timeout;
+ fifo_timeout = uart_fifo_timeout(port);
+ if (timeout == 0 || timeout > 2 * fifo_timeout)
+ timeout = 2 * fifo_timeout;
}
expire = jiffies + timeout;
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 5518b70177b3..373783487b2e 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -231,7 +231,6 @@ struct uart_port {
int hw_stopped; /* sw-assisted CTS flow state */
unsigned int mctrl; /* current modem ctrl settings */
- unsigned int timeout; /* character-based timeout */
unsigned int frame_time; /* frame timing in ns */
unsigned int type; /* port type */
const struct uart_ops *ops;
@@ -334,10 +333,23 @@ unsigned int uart_get_baud_rate(struct uart_port *port, struct ktermios *termios
unsigned int max);
unsigned int uart_get_divisor(struct uart_port *port, unsigned int baud);
+/*
+ * Calculates FIFO drain time.
+ */
+static inline unsigned long uart_fifo_timeout(struct uart_port *port)
+{
+ u64 fifo_timeout = (u64)READ_ONCE(port->frame_time) * port->fifosize;
+
+ /* Add .02 seconds of slop */
+ fifo_timeout += 20 * NSEC_PER_MSEC;
+
+ return max(nsecs_to_jiffies(fifo_timeout), 1UL);
+}
+
/* Base timer interval for polling */
static inline int uart_poll_timeout(struct uart_port *port)
{
- int timeout = port->timeout;
+ int timeout = uart_fifo_timeout(port);
return timeout > 6 ? (timeout / 2 - 2) : 1;
}
--
tg: (65534736d9a5..) serial/drop-timeout (depends on: tty-next)
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