linux-kernel - Re: [PATCH 1/2] tty: n_gsm: Fix long delays with control frame timeouts in ADM mode

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Message-ID: <20180408090259.GA8185@amd>
Date:   Sun, 8 Apr 2018 11:02:59 +0200
From:   Pavel Machek <pavel@....cz>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Alan Cox <alan@...yncelyn.cymru>,
        Dan Williams <dcbw@...hat.com>,
        Jiri Prchal <jiri.prchal@...ignal.cz>,
        Jiri Slaby <jslaby@...e.cz>, Marcel Partap <mpartap@....net>,
        Merlijn Wajer <merlijn@...zup.org>,
        Michael Nazzareno Trimarchi <michael@...rulasolutions.com>,
        Michael Scott <michael.scott@...aro.org>,
        Peter Hurley <peter@...leysoftware.com>,
        Russ Gorby <russ.gorby@...el.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sebastian Reichel <sre@...nel.org>
Subject: Re: [PATCH 1/2] tty: n_gsm: Fix long delays with control frame
 timeouts in ADM mode

Hi!

> Commit ea3d8465ab9b ("tty: n_gsm: Allow ADM response in addition to UA for
> control dlci") added support for DLCI to stay in Asynchronous Disconnected
> Mode (ADM). But we still get long delays waiting for commands to other
> DLCI to complete:
> 
> --> 5) C: SABM(P)
> Q>  0) C: UIH(F)
> Q>  0) C: UIH(F)
> Q>  0) C: UIH(F)
> ...
> 
> This happens because gsm_control_send() sets cretries timer to T2 that is
> by default set to 34. This will cause resend for T2 times for the control
> frame. In ADM mode, we will never get a response so the control frame, so
> retries are just delaying all the commands.
> 
> Let's fix the issue by setting DLCI_MODE_ADM flag after detecting the ADM
> mode for the control DLCI. Then we can use that in gsm_control_send() to
> set retries to 1. This means the control frame will be sent once allowing
> the other end at an opportunity to switch from ADM to ABM mode.
> 
> Note that retries will be decremented in gsm_control_retransmit() so
> we don't want to set it to 0 here.

Thanks!

I guess I'd like to test this on Droid4; there are fso-gsm0710muxd and
gsm0710muxd packages in Debian, but I assume those do multiplexing in
userspace and thus are not suitable?

Do you have a tool to use and a script?

Thanks and best regards,
									Pavel
									
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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