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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 D9D51C4743F for ; Mon, 7 Jun 2021 10:54:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC42761107 for ; Mon, 7 Jun 2021 10:54:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230178AbhFGK4c (ORCPT ); Mon, 7 Jun 2021 06:56:32 -0400 Received: from mo4-p01-ob.smtp.rzone.de ([85.215.255.54]:26085 "EHLO mo4-p01-ob.smtp.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230131AbhFGK4c (ORCPT ); Mon, 7 Jun 2021 06:56:32 -0400 ARC-Seal: i=1; a=rsa-sha256; t=1623063273; cv=none; d=strato.com; s=strato-dkim-0002; b=U2IUTV4H2dq/GOzdZ1PFhSHiW/DFDHabhUWoHotRiSopxeSxdD3CknsWYjXK/iyJ5d g0tUFLDAtEGdsJJih0mKnMqOOITAnt+2tMmWNyLtULLvgcgG3qrcgrO+JZvmWNKeVeZR Zw3p5j4QzPSOSec9y/6V91ZVYvtE5HV+k17dI1uWo7TfN4nU/EBgcbsLzU/i+imgpssX IHMpB2hqqfPKV7DDOZFAi/WcoEW5RoGsxiLuDUzgnCoKmjFoxGWanGm0cpKFaHfCP2O5 vOLFBEMzff7Z/ZfbdOMvnNBbMY6F0e+RkTz1UDJYN+FiiyoNsGnW0pnafcMkJdPtqUOD MUFA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; t=1623063273; s=strato-dkim-0002; d=strato.com; h=In-Reply-To:References:Message-ID:Subject:Cc:To:From:Date:Cc:Date: From:Subject:Sender; bh=hdm4hBggGM17oX9y9jwL4+IJ8JgrHVXkX3Pxwr0GLLs=; b=llKxed79twSurxjLYd+XhpLK+3gwVXUr2LjUEkXsRT6QxVLFha+kC1ayfyEdCKzaP5 XkSmH9ZEOln+9CucDNWkJZgwraYOWpc4BjwpAbnSdRDcqS40NaceH0PghFATNcq7E3oZ dAByynKkLSDY0+LBo2L8wamPavUxmmNxM0sRVwlOw2W/oee9MBLB37WfEp7GToypxByC b0MpNVUeUnJPvYOcX979gI04zqrC8iI0tqQt0c2S/bTHq6USlN3aA+5xPdd2WVUkLOph r7Yqcy6tTIZ2XS19uJBeeQqwt/1n5nxZDvnYPraABv5WcJdvCIehBapcH+6nh06Xyfg1 HSLg== ARC-Authentication-Results: i=1; strato.com; dkim=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1623063273; s=strato-dkim-0002; d=gerhold.net; h=In-Reply-To:References:Message-ID:Subject:Cc:To:From:Date:Cc:Date: From:Subject:Sender; bh=hdm4hBggGM17oX9y9jwL4+IJ8JgrHVXkX3Pxwr0GLLs=; b=K1Wv6NVTRhrYMo3X9PrgJkrYiuG5gNRC3xJwxdeb4qRSmV+7FHgMS4E+3k/FnMvtFQ naha4v4dJ9qZkH5wZx1Sgju9/NG9QxVv5qLoNumhtPP4Fo2JcKF9cJPFj7dWPD/fX8oB cjo0FApUYcHA/ZLoZBFbmu8Dkz1Pod16mHJI50LNKTfHewTVTVCp39p90CXK+ucWx29+ K5IMSYBSgtDHXSR8L9GYdHv3vuJm/TqI3tOE7vVtmrbx7uHL6vt/sXr0qEV5wsauvMdQ DVPlD7YouK6AubTlwK/J5vuRx1/56A03C30q2psP5A3yik2Vzl9dLTjkqkY4+8EgWhLz m88g== Authentication-Results: strato.com; dkim=none X-RZG-AUTH: ":P3gBZUipdd93FF5ZZvYFPugejmSTVR2nRPhVOQ/OcYgojyw4j34+u26zEodhPgRDZ8j7Ic/BBg==" X-RZG-CLASS-ID: mo00 Received: from gerhold.net by smtp.strato.de (RZmta 47.27.2 DYNA|AUTH) with ESMTPSA id y01375x57AsWTsN (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate); Mon, 7 Jun 2021 12:54:32 +0200 (CEST) Date: Mon, 7 Jun 2021 12:54:27 +0200 From: Stephan Gerhold To: Loic Poulain Cc: Bjorn Andersson , Aleksander Morgado , Network Development , linux-remoteproc@vger.kernel.org, linux-arm-msm , "David S. Miller" , Jakub Kicinski , Ohad Ben-Cohen , Mathieu Poirier Subject: Re: [RFC] Integrate RPMSG/SMD into WWAN subsystem Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Hi Loic, On Mon, Jun 07, 2021 at 11:27:07AM +0200, Loic Poulain wrote: > On Sat, 5 Jun 2021 at 11:25, Stephan Gerhold wrote: > > On Fri, Jun 04, 2021 at 11:11:45PM +0200, Loic Poulain wrote: > > > On Wed, 2 Jun 2021 at 20:20, Stephan Gerhold wrote: > > > > I've been thinking about creating some sort of "RPMSG" driver for the > > > > new WWAN subsystem; this would be used as a QMI/AT channel to the > > > > integrated modem on some older Qualcomm SoCs such as MSM8916 and MSM8974. > > > > > > > > It's easy to confuse all the different approaches that Qualcomm has to > > > > talk to their modems, so I will first try to briefly give an overview > > > > about those that I'm familiar with: > > > > > > > > --- > > > > There is USB and MHI that are mainly used to talk to "external" modems. > > > > > > > > For the integrated modems in many Qualcomm SoCs there is typically > > > > a separate control and data path. They are not really related to each > > > > other (e.g. currently no common parent device in sysfs). > > > > > > > > For the data path (network interface) there is "IPA" (drivers/net/ipa) > > > > on newer SoCs or "BAM-DMUX" on some older SoCs (e.g. MSM8916/MSM8974). > > > > I have a driver for BAM-DMUX that I hope to finish up and submit soon. > > > > > > > > The connection is set up via QMI. The messages are either sent via > > > > a shared RPMSG channel (net/qrtr sockets in Linux) or via standalone > > > > SMD/RPMSG channels (e.g. "DATA5_CNTL" for QMI and "DATA1" for AT). > > > > > > > > This gives a lot of possible combinations like BAM-DMUX+RPMSG > > > > (MSM8916, MSM8974), or IPA+QRTR (SDM845) but also other funny > > > > combinations like IPA+RPMSG (MSM8994) or BAM-DMUX+QRTR (MSM8937). > > > > > > > > Simply put, supporting all these in userspace like ModemManager > > > > is a mess (Aleksander can probably confirm). > > > > It would be nice if this could be simplified through the WWAN subsystem. > > > > > > > > It's not clear to me if or how well QRTR sockets can be mapped to a char > > > > device for the WWAN subsystem, so for now I'm trying to focus on the > > > > standalone RPMSG approach (for MSM8916, MSM8974, ...). > > > > --- > > > > > > > > Currently ModemManager uses the RPMSG channels via the rpmsg-chardev > > > > (drivers/rpmsg/rpmsg_char.c). It wasn't my idea to use it like this, > > > > I just took that over from someone else. Realistically speaking, the > > > > current approach isn't too different from the UCI "backdoor interface" > > > > approach that was rejected for MHI... > > > > > > > > I kind of expected that I can just trivially copy some code from > > > > rpmsg_char.c into a WWAN driver since they both end up as a simple char > > > > device. But it looks like the abstractions in wwan_core are kind of > > > > getting in the way here... As far as I can tell, they don't really fit > > > > together with the RPMSG interface. > > > > > > > > For example there is rpmsg_send(...) (blocking) and rpmsg_trysend(...) > > > > (non-blocking) and even a rpmsg_poll(...) [1] but I don't see a way to > > > > get notified when the TX queue is full or no longer full so I can call > > > > wwan_port_txon/off(). > > > > > > > > Any suggestions or other thoughts? > > > > > > It would be indeed nice to get this in the WWAN framework. > > > I don't know much about rpmsg but I think it is straightforward for > > > the RX path, the ept_cb can simply forward the buffers to > > > wwan_port_rx. > > > > Right, that part should be straightforward. > > > > > For tx, simply call rpmsg_trysend() in the wwan tx > > > callback and don't use the txon/off helpers. In short, keep it simple > > > and check if you observe any issues. > > > > > > > I'm not sure that's a good idea. This sounds like exactly the kind of > > thing that might explode later just because I don't manage to get the > > TX queue full in my tests. In that case, writing to the WWAN char dev > > would not block, even if O_NONBLOCK is not set. > > Right, if you think it could be a problem, you can always implement a > more complex solution like calling rpmsg_send from a > workqueue/kthread, and only re-enable tx once rpmsg_send returns. > I did run into trouble when I tried to stream lots of data into the WWAN char device (e.g. using dd). However, in practice (with ModemManager) I did not manage to cause such issues yet. Personally, I think it's something we should get right, just to avoid trouble later (like "modem suddenly stops working"). Right now I extended the WWAN port ops a bit so I tells me if the write should be non-blocking or blocking and so I can call rpmsg_poll(...). But having some sort of workqueue also sounds like it could work quite well, thanks for the suggestion! Will think about it some more, or I might post what I have right now so you can take a look. > > > > But I think you're right that it's probably easiest if I start with > > that, see if I can get anything working at all ... > > > > > And for sure you can propose changes in the WWAN framework if you > > > think something is missing to support your specific case. > > > > > > > ... and then we can discuss that further on a RFC PATCH or something > > like that. Does that sound good to you? > > Yes, you can submit the series, no need to be RFC IMHO, this thread is > already your RFC. > I kind of see "RFC" like a "I'm not sure if the approach taken here is really a good idea" and my current patch set currently still fits that criteria. But at the end it's just a strange prefix for the mail subject so it shouldn't matter too much. :) Thanks! Stephan