diff options
| author | Johan Hovold <johan@kernel.org> | 2017-01-25 15:35:20 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-02-26 11:07:51 +0100 |
| commit | cfad0817222d0c2cf1f2a848054aa4a6a943874b (patch) | |
| tree | 44cf9ec9247aa57e48a7d4c1951cb14db8725510 | |
| parent | af82872b65e06403a4d7ab354eef96870d192889 (diff) | |
USB: serial: ftdi_sio: fix extreme low-latency setting
commit c6dce2626606ef16434802989466636bc28c1419 upstream.
Since commit 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY
flag") the FTDI driver has been using a receive latency-timer value of
1 ms instead of the device default of 16 ms.
The latency timer is used to periodically empty a non-full receive
buffer, but a status header is always sent when the timer expires
including when the buffer is empty. This means that a two-byte bulk
message is received every millisecond also for an otherwise idle port as
long as it is open.
Let's restore the pre-2009 behaviour which reduces the rate of the
status messages to 1/16th (e.g. interrupt frequency drops from 1 kHz to
62.5 Hz) by not setting ASYNC_LOW_LATENCY by default.
Anyone willing to pay the price for the minimum-latency behaviour should
set the flag explicitly instead using the TIOCSSERIAL ioctl or a tool
such as setserial (e.g. setserial /dev/ttyUSB0 low_latency).
Note that since commit 0cbd81a9f6ba ("USB: ftdi_sio: remove
tty->low_latency") the ASYNC_LOW_LATENCY flag has no other effects but
to set a minimal latency timer.
Reported-by: Antoine Aubert <a.aubert@overkiz.com>
Fixes: 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY flag")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/usb/serial/ftdi_sio.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c index 848e4af6e10e..46d5d8cd4c79 100644 --- a/drivers/usb/serial/ftdi_sio.c +++ b/drivers/usb/serial/ftdi_sio.c @@ -1807,8 +1807,6 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port) mutex_init(&priv->cfg_lock); - priv->flags = ASYNC_LOW_LATENCY; - if (quirk && quirk->port_probe) quirk->port_probe(priv); |