2021-04-21 12:00:19

by Johan Hovold

Subject: [PATCH 23/26] serial: sunsu: drop low-latency workaround

The sunsu driver has been carrying a workaround for the infamous
low_latency behaviour of tty_flip_buffer_push() by dropping and
reacquiring the port lock in the interrupt handler since 2004.

Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks around.

Cc: "David S. Miller" <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
---
drivers/tty/serial/sunsu.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/drivers/tty/serial/sunsu.c b/drivers/tty/serial/sunsu.c
index 319e5ceb6130..12c2468f2b0e 100644
--- a/drivers/tty/serial/sunsu.c
+++ b/drivers/tty/serial/sunsu.c
@@ -466,12 +466,8 @@ static irqreturn_t sunsu_serial_interrupt(int irq, void *dev_id)
if (status & UART_LSR_THRE)
transmit_chars(up);

- spin_unlock_irqrestore(&up->port.lock, flags);
-
tty_flip_buffer_push(&up->port.state->port);

- spin_lock_irqsave(&up->port.lock, flags);
-
} while (!(serial_in(up, UART_IIR) & UART_IIR_NO_INT));

spin_unlock_irqrestore(&up->port.lock, flags);
--
2.26.3

2021-04-22 00:59:46

by David Miller

Subject: Re: [PATCH 23/26] serial: sunsu: drop low-latency workaround

From: Johan Hovold <[email protected]>
Date: Wed, 21 Apr 2021 11:55:06 +0200

> The sunsu driver has been carrying a workaround for the infamous
> low_latency behaviour of tty_flip_buffer_push() by dropping and
> reacquiring the port lock in the interrupt handler since 2004.
>
> Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
> tty_flip_buffer_push() always schedules a work item to push data to the
> line discipline and there's no need to keep any low_latency hacks around.
>
> Cc: "David S. Miller" <[email protected]>
> Signed-off-by: Johan Hovold <[email protected]>

Acked-by: David S. Miller <[email protected]>