On 03/20/2018 09:52 PM, Jeremy Kerr wrote:
This change adds a flag to indicate that a UART is has an external means
of synchronising its FIFO, without needing CTSRTS or XON/XOFF.
This allows us to use the throttle/unthrottle callbacks, without having
to claim other methods of flow control.
This series fixed extremely heavy cpu usage we were getting with a lot
of traffic coming in on the console. System is usable again with console
getting hammered.
Tested-by: Eddie James <eajames@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jeremy Kerr <jk@xxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 4 ++--
include/linux/serial_core.h | 1 +
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f534a40aebde..8f3dfc8b5307 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -678,7 +678,7 @@ static void uart_throttle(struct tty_struct *tty)
if (C_CRTSCTS(tty))
mask |= UPSTAT_AUTORTS;
- if (port->status & mask) {
+ if (port->status & (mask | UPSTAT_SYNC_FIFO)) {
port->ops->throttle(port);
mask &= ~port->status;
}
@@ -707,7 +707,7 @@ static void uart_unthrottle(struct tty_struct *tty)
if (C_CRTSCTS(tty))
mask |= UPSTAT_AUTORTS;
- if (port->status & mask) {
+ if (port->status & (mask | UPSTAT_SYNC_FIFO)) {
port->ops->unthrottle(port);
mask &= ~port->status;
}
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 1775500294bb..bf600ae0290d 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -232,6 +232,7 @@ struct uart_port {
#define UPSTAT_AUTORTS ((__force upstat_t) (1 << 2))
#define UPSTAT_AUTOCTS ((__force upstat_t) (1 << 3))
#define UPSTAT_AUTOXOFF ((__force upstat_t) (1 << 4))
+#define UPSTAT_SYNC_FIFO ((__force upstat_t) (1 << 5))
int hw_stopped; /* sw-assisted CTS flow state */
unsigned int mctrl; /* current modem ctrl settings */
--
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