Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756582Ab2JWCer (ORCPT ); Mon, 22 Oct 2012 22:34:47 -0400 Received: from mailout39.mail01.mtsvc.net ([216.70.64.83]:55333 "EHLO n12.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753800Ab2JWCeq (ORCPT ); Mon, 22 Oct 2012 22:34:46 -0400 Message-ID: <1350959679.2621.55.camel@thor> Subject: Re: [PATCH 0/1] staging: Add firewire-serial driver From: Peter Hurley To: Greg Kroah-Hartman Cc: Stefan Richter , devel@driverdev.osuosl.org, linux1394-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Date: Mon, 22 Oct 2012 22:34:39 -0400 In-Reply-To: <20121022224505.GD24489@kroah.com> References: <1350565015.23730.4.camel@thor> <20121022224505.GD24489@kroah.com> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.2.4-0build1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Authenticated-User: 125194 peter@hurleysoftware.com X-MT-ID: 8fa290c2a27252aacf65dbc4a42f3ce3735fb2a4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2692 Lines: 58 On Mon, 2012-10-22 at 15:45 -0700, Greg Kroah-Hartman wrote: > On Thu, Oct 18, 2012 at 08:56:55AM -0400, Peter Hurley wrote: > > Please consider this serial driver for review for submission to staging. > > The firewire-serial driver implements TTY over IEEE 1394. In its default > > configuration, it creates 4 TTY devices and one loopback device per > > firewire card (respectively, named fwtty~fwtty and fwloop). > > > > Currently, the TTY devices auto-connect to every cabled peer (the TODO > > list includes plans for providing a sysfs interface to control virtual > > cabling with whitelist/blacklist support per GUID). > > > > Efforts are still ongoing for a companion console driver, with plans to > > eventually add early_printk & kgdb support (via additional drivers). > > > > Some issues did arise with both the TTY and Firewire subsystems which > > are noted in the TODO file. Please review these workarounds. > > > > Peter Hurley (1): > > staging: fwserial: Add TTY-over-Firewire serial driver > > I'd like to get an Ack from Stefan here, before I'll add this to the > staging tree. Of course. Jiri's newest series ("TTY buffer in tty_port and other stuff") does break this driver, so I'll need to resubmit to address those changes. Two of the workarounds mentioned in the TODO are related to the tty_buffer interface; specifically, 1. The ldisc drops the contents of tty_buffer on hangup (rather than waiting for completion). Maybe for other devices this isn't so noticeable because the ldisc can mostly keep up with the device, but on firewire the ldisc lags well behind. Right now, this driver works around this by holding off the hangup until the ldisc empties the tty_buffer. The driver determines how much data is still left in the tty_buffer by walking the flip buffers. 2. Because this driver can fill the entire tty_buffer (64K +) before the ldisc even runs once, this driver has to self-throttle when feeding the tty_buffer. So as not to drop data, the driver has to know when a watermark is reached in the tty_buffer, to ensure that in-flight + already-accepted data can safely be moved to what remains avail in the tty_buffer. (The tty_buffer maxs at 64K). Currently, the avail level in the tty_buffer is computed by this driver (in the same manner as tty_buffer_alloc()). Eventually, I'd like to move these changes into tty_buffer but I wanted to present the use case first. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/