From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751901AbeA1OeI convert rfc822-to-8bit (ORCPT ); Sun, 28 Jan 2018 09:34:08 -0500 Received: from inx.pm.waw.pl ([91.202.125.194]:49603 "EHLO inx.pm.waw.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751496AbeA1OeG (ORCPT ); Sun, 28 Jan 2018 09:34:06 -0500 From: Krzysztof Halasa To: Denis Du Cc: David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Carrier detect ok, don't turn off negotiation References: <751079597.1884905.1516121905374.ref@mail.yahoo.com> <751079597.1884905.1516121905374@mail.yahoo.com> <20180122.152513.1108868799788445512.davem@davemloft.net> <998451043.3408644.1516727290310@mail.yahoo.com> Date: Sun, 28 Jan 2018 15:24:16 +0100 In-Reply-To: <998451043.3408644.1516727290310@mail.yahoo.com> (Denis Du's message of "Tue, 23 Jan 2018 17:08:10 +0000 (UTC)") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Denis Du writes: >>>From the above code, I can get that only Carrier have some change, it > will restart the protocol by hdlc_proto_start(dev);and thus the timer, > the previous timer expired due to protocol fail. > > If carrier keep no change by if (hdlc->carrier == on) >         goto carrier_exit; /* no change in DCD line level */It will do > nothing, not start any new protocol and thus the timer. Sorry about being late, just returned home and am trying to get all the backlogs under control. I remember the PPP standard is a bit cloudy about the possible issue, but the latter indeed exists (the PPP state machine was written directly to STD-51). There is related (more visible in practice, though we aren't affected) issue of "active" vs "passive" mode (hdlc_ppp.c is "active", and two "passives" wouldn't negotiate at all). Anyway the problem is real (though not very visible in practice, especially on relatively modern links rather than 300 or 1200 bps dialup connections) and should be fixed. Looking at the patch, my first impression is it makes the code differ from STD-51 a little bit. On the other hand, perhaps applying it as is and forgetting about the issue is the way to go. Ideally, I think the negotiation failure should end up (optionally, in addition to the current behavior) in some configurable sleep, then the negotiation should restart. If it's worth the effort at this point, I don't know. Perhaps I could look at this later, but no promises (this requires pulling on and setting up some legacy hardware). Anyway, since the patch is safe and can solve an existing problem: Acked-by: Krzysztof Halasa -- Krzysztof Halasa