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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 Date: Tue, 18 Jun 2019 15:15:42 -0600 From: Subash Abhinov Kasiviswanathan To: Arnd Bergmann 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190618_141547_350723_8070B35A X-CRM114-Status: GOOD ( 24.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: DTML , syadagir@codeaurora.org, Eric Caruso , David Miller , Dan Williams , linux-arm-msm@vger.kernel.org, Ilias Apalodimas , Linux Kernel Mailing List , evgreen@chromium.org, Bjorn Andersson , Networking , Linux ARM , Alex Elder , Johannes Berg , linux-soc@vger.kernel.org, abhishek.esse@gmail.com, cpratapa@codeaurora.org, Ben Chan Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel