From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:33878 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751283AbdBWU6I (ORCPT ); Thu, 23 Feb 2017 15:58:08 -0500 Subject: Patch "USB: serial: ftdi_sio: fix extreme low-latency setting" has been added to the 4.4-stable tree To: johan@kernel.org, a.aubert@overkiz.com, gregkh@linuxfoundation.org Cc: , From: Date: Thu, 23 Feb 2017 21:56:44 +0100 Message-ID: <148788340456222@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled USB: serial: ftdi_sio: fix extreme low-latency setting to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: usb-serial-ftdi_sio-fix-extreme-low-latency-setting.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From c6dce2626606ef16434802989466636bc28c1419 Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Wed, 25 Jan 2017 15:35:20 +0100 Subject: USB: serial: ftdi_sio: fix extreme low-latency setting From: Johan Hovold 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: Greg Kroah-Hartman --- drivers/usb/serial/ftdi_sio.c | 2 -- 1 file changed, 2 deletions(-) --- 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 us mutex_init(&priv->cfg_lock); - priv->flags = ASYNC_LOW_LATENCY; - if (quirk && quirk->port_probe) quirk->port_probe(priv); Patches currently in stable-queue which might be from johan@kernel.org are queue-4.4/usb-serial-ftdi_sio-fix-modem-status-error-handling.patch queue-4.4/usb-serial-cp210x-add-new-ids-for-ge-bx50v3-boards.patch queue-4.4/usb-serial-ark3116-fix-register-accessor-error-handling.patch queue-4.4/usb-serial-digi_acceleport-fix-oob-data-sanity-check.patch queue-4.4/usb-serial-ftdi_sio-fix-line-status-over-reporting.patch queue-4.4/usb-serial-ftdi_sio-fix-extreme-low-latency-setting.patch queue-4.4/usb-serial-spcp8x5-fix-modem-status-handling.patch queue-4.4/usb-serial-opticon-fix-cts-retrieval-at-open.patch queue-4.4/usb-serial-mos7840-fix-another-null-deref-at-open.patch