From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9682C04AB6 for ; Fri, 31 May 2019 21:12:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BABD26F2F for ; Fri, 31 May 2019 21:12:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727680AbfEaVMi (ORCPT ); Fri, 31 May 2019 17:12:38 -0400 Received: from mail-qt1-f196.google.com ([209.85.160.196]:46256 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727005AbfEaVMi (ORCPT ); Fri, 31 May 2019 17:12:38 -0400 Received: by mail-qt1-f196.google.com with SMTP id z19so2594676qtz.13; Fri, 31 May 2019 14:12:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AZptDCZbtMb0PQHhtVnS/aF9UysKMAzgtneB0+7FC+I=; b=fXeIVN34xckBCndWGV5hGmm7h9qaopS1ztQocf+iEL8dlB9iQt0WrO6Yqw1j2BjNb4 Av4aWOR5F3XWolPuq/+zl1aGyfviRFwmvriCnSiYMdSsYpAepBkUg1CvBsHjU3NogKRk qywUvfnhntKZcKN3oIjEAq25M2rGaUwdJGIs2IlUg71Y9whAuZRB1Lbi6HT1mGMfh9um 8fT6i35u7AqX3tfVpPvDwIvNbvC7gecbUp7fn7dATjugICJY9ql6Sd0egP9WZlRWBs5f Vumh8D/d/eG5WKMOCvGfk/S5wmyGuCgK+Ipl9NoCjOiviCIl3VE5SEPhB+3YecFl9vag Y1LQ== X-Gm-Message-State: APjAAAWs2RUKSTHYkiK0O9znTh8lDDX2DraweKL+E6uhqk/KxX2xvOgT MLs2idA2MFdU6ks31xBK3743tMAen4Q9tIs8RjR3Jm9i X-Google-Smtp-Source: APXvYqzHvUnfa6x/YLh/Fjn3Tw3E+yBquiW3NroCyGZFdVC85oGAnHKEDZucf7nAm9xpQNUD3gkU2OGRWDNqkRg6xhY= X-Received: by 2002:aed:3e7c:: with SMTP id m57mr6159988qtf.204.1559337157081; Fri, 31 May 2019 14:12:37 -0700 (PDT) MIME-Version: 1.0 References: <20190531035348.7194-1-elder@linaro.org> <065c95a8-7b17-495d-f225-36c46faccdd7@linaro.org> In-Reply-To: From: Arnd Bergmann Date: Fri, 31 May 2019 23:12:20 +0200 Message-ID: Subject: Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver To: Alex Elder Cc: Dan Williams , David Miller , Bjorn Andersson , Ilias Apalodimas , evgreen@chromium.org, Ben Chan , Eric Caruso , cpratapa@codeaurora.org, syadagir@codeaurora.org, Subash Abhinov Kasiviswanathan , abhishek.esse@gmail.com, Networking , DTML , Linux Kernel Mailing List , linux-soc@vger.kernel.org, Linux ARM , linux-arm-msm@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, May 31, 2019 at 10:47 PM Alex Elder wrote: > On 5/31/19 2:19 PM, Arnd Bergmann wrote: > > On Fri, May 31, 2019 at 6:36 PM Alex Elder wrote: > >> On 5/31/19 9:58 AM, Dan Williams wrote: > >>> On Thu, 2019-05-30 at 22:53 -0500, Alex Elder wrote: > > > > Does this mean that IPA can only be used to back rmnet, and rmnet > > can only be used on top of IPA, or can or both of them be combined > > with another driver to talk to instead? > > No it does not mean that. > > As I understand it, one reason for the rmnet layer was to abstract > the back end, which would allow using a modem, or using something > else (a LAN?), without exposing certain details of the hardware. > (Perhaps to support multiplexing, etc. without duplicating that > logic in two "back-end" drivers?) > > To be perfectly honest, at first I thought having IPA use rmnet > was a cargo cult thing like Dan suggested, because I didn't see > the benefit. I now see why one would use that pass-through layer > to handle the QMAP features. > > But back to your question. The other thing is that I see no > reason the IPA couldn't present a "normal" (non QMAP) interface > for a modem. It's something I'd really like to be able to do, > but I can't do it without having the modem firmware change its > configuration for these endpoints. My access to the people who > implement the modem firmware has been very limited (something > I hope to improve), and unless and until I can get corresponding > changes on the modem side to implement connections that don't > use QMAP, I can't implement such a thing. Why would that require firmware changes? What I was thinking here is to turn the bits of the rmnet driver that actually do anything interesting on the headers into a library module (or a header file with inline functions) that can be called directly by the ipa driver, keeping the protocol unchanged. > > Always passing data from one netdev to another both ways > > sounds like it introduces both direct CPU overhead, and > > problems with flow control when data gets buffered inbetween. > > My impression is the rmnet driver is a pretty thin layer, > so the CPU overhead is probably not that great (though > deaggregating a message is expensive). I agree with you > on the flow control. The CPU overhead I mean is not from executing code in the rmnet driver, but from passing packets through the network stack between the two drivers, i.e. adding each frame to a queue and taking it back out. I'm not sure how this ends up working in reality but from a first look it seems like we might bounce in an out of the softirq handler inbetween. Arnd