Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932070AbdCFJZF (ORCPT ); Mon, 6 Mar 2017 04:25:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:37284 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753279AbdCFJNz (ORCPT ); Mon, 6 Mar 2017 04:13:55 -0500 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Johan Hovold , Jiri Slaby Subject: [PATCH 3.12 081/113] USB: serial: ftdi_sio: fix extreme low-latency setting Date: Mon, 6 Mar 2017 10:11:45 +0100 Message-Id: <7cf4bcb6f3bff2f8f73f0a2c5b8e9572e44a6e07.1488791431.git.jslaby@suse.cz> X-Mailer: git-send-email 2.12.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1932 Lines: 53 From: Johan Hovold 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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 Fixes: 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY flag") Signed-off-by: Johan Hovold Signed-off-by: Jiri Slaby --- drivers/usb/serial/ftdi_sio.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c index 5ed104787474..e2e564a071fc 100644 --- a/drivers/usb/serial/ftdi_sio.c +++ b/drivers/usb/serial/ftdi_sio.c @@ -1829,8 +1829,6 @@ 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); -- 2.12.0