From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eddie James Date: Fri, 23 Mar 2018 10:50:26 -0500 Subject: [PATCH 1/5] serial: Introduce UPSTAT_SYNC_FIFO for synchronised FIFOs In-Reply-To: <20180321025241.19785-2-jk@ozlabs.org> References: <20180321025241.19785-1-jk@ozlabs.org> <20180321025241.19785-2-jk@ozlabs.org> Message-ID: <2708b9bf-cf8b-a98e-d64b-abb1c90a927f@linux.vnet.ibm.com> List-Id: To: linux-aspeed@lists.ozlabs.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 > > Signed-off-by: Jeremy Kerr > --- > 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 */