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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 8C114C31E5B for ; Tue, 18 Jun 2019 21:15:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5E98B204FD for ; Tue, 18 Jun 2019 21:15:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="IVOJN7iw"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="TOVI6NUY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730727AbfFRVPs (ORCPT ); Tue, 18 Jun 2019 17:15:48 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:55442 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730350AbfFRVPs (ORCPT ); Tue, 18 Jun 2019 17:15:48 -0400 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id A466560FED; Tue, 18 Jun 2019 21:15:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1560892546; bh=YZxqpwNwj9xP1mVakWl4GnRWhuxU+h/l52kLOjkWX3Y=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=IVOJN7iw7SLfamnGPFOAHWKxlR24qZGI+fJflD1GHP+Oo/BkYwgUJIRH8PyDeOjIX yWdNc+O9P4dYI5N0wCG8AHfCVvLmPw/X/UKLIfyjXkZNDQzm9mCb+/zEFpUXJLPOBP 01BzNaRPwCzmRCWihbrOMK4u18fWzfMXFHFzCzHg= Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.codeaurora.org (Postfix) with ESMTP id 3E048608BA; Tue, 18 Jun 2019 21:15:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1560892544; bh=YZxqpwNwj9xP1mVakWl4GnRWhuxU+h/l52kLOjkWX3Y=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TOVI6NUYG8I82CcnESxWEYgB0kYG+0CZ96pkTfQAcneB00XUWHiCLDk9M8clfZqdU enPHMCLJDTDCNtKey6d8+AOJmN1NmXdJC6F943mG9WsGQugpIFqi8+l8PUVpxBt6uk U7rdCNWQ7xeD9PerfSVkAPcLATq9szGad+VzOXQU= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 18 Jun 2019 15:15:42 -0600 From: Subash Abhinov Kasiviswanathan To: Arnd Bergmann Cc: Johannes Berg , Alex Elder , abhishek.esse@gmail.com, Ben Chan , Bjorn Andersson , cpratapa@codeaurora.org, David Miller , Dan Williams , DTML , Eric Caruso , evgreen@chromium.org, Ilias Apalodimas , Linux ARM , linux-arm-msm@vger.kernel.org, Linux Kernel Mailing List , linux-soc@vger.kernel.org, Networking , syadagir@codeaurora.org Subject: Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver In-Reply-To: References: <380a6185-7ad1-6be0-060b-e6e5d4126917@linaro.org> <066e9b39f937586f0f922abf801351553ec2ba1d.camel@sipsolutions.net> <613cdfde488eb23d7207c7ba6258662702d04840.camel@sipsolutions.net> Message-ID: <6c70950d0c78bc02a3d016918ec3929e@codeaurora.org> X-Sender: subashab@codeaurora.org User-Agent: Roundcube Webmail/1.2.5 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019-06-18 14:55, Arnd Bergmann wrote: > On Tue, Jun 18, 2019 at 10:36 PM Johannes Berg > wrote: >> >> On Tue, 2019-06-18 at 21:59 +0200, Arnd Bergmann wrote: >> > >> > From my understanding, the ioctl interface would create the lower >> > netdev after talking to the firmware, and then user space would use >> > the rmnet interface to create a matching upper-level device for that. >> > This is an artifact of the strong separation of ipa and rmnet in the >> > code. >> >> Huh. But if rmnet has muxing, and IPA supports that, why would you >> ever >> need multiple lower netdevs? > > From my reading of the code, there is always exactly a 1:1 relationship > between an rmnet netdev an an ipa netdev. rmnet does the encapsulation/ > decapsulation of the qmap data and forwards it to the ipa netdev, > which then just passes data through between a hardware queue and > its netdevice. > There is a n:1 relationship between rmnet and IPA. rmnet does the de-muxing to multiple netdevs based on the mux id in the MAP header for RX packets and vice versa. > [side note: on top of that, rmnet also does "aggregation", which may > be a confusing term that only means transferring multiple frames > at once] > >> > ipa definitely has multiple hardware queues, and the Alex' >> > driver does implement the data path on those, just not the >> > configuration to enable them. >> >> OK, but perhaps you don't actually have enough to use one for each >> session? > > I'm lacking the terminology here, but what I understood was that > the netdev and queue again map to a session. > >> > Guessing once more, I suspect the the XON/XOFF flow control >> > was a workaround for the fact that rmnet and ipa have separate >> > queues. The hardware channel on IPA may fill up, but user space >> > talks to rmnet and still add more frames to it because it doesn't >> > know IPA is busy. >> > >> > Another possible explanation would be that this is actually >> > forwarding state from the base station to tell the driver to >> > stop sending data over the air. >> >> Yeah, but if you actually have a hardware queue per upper netdev then >> you don't really need this - you just stop the netdev queue when the >> hardware queue is full, and you have flow control automatically. >> >> So I really don't see any reason to have these messages going back and >> forth unless you plan to have multiple sessions muxed on a single >> hardware queue. > Hardware may flow control specific PDNs (rmnet interfaces) based on QoS - not necessarily only in case of hardware queue full. > Sure, I definitely understand what you mean, and I agree that would > be the right way to do it. All I said is that this is not how it was > done > in rmnet (this was again my main concern about the rmnet design > after I learned it was required for ipa) ;-) > > Arnd -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project