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[104.57.184.186]) by smtp.gmail.com with ESMTPSA id d3sm652338ooi.42.2021.02.10.14.08.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Feb 2021 14:08:41 -0800 (PST) Date: Wed, 10 Feb 2021 16:08:39 -0600 From: Bjorn Andersson To: Jakub Kicinski Cc: Manivannan Sadhasivam , Aleksander Morgado , Loic Poulain , Greg KH , David Miller , linux-arm-msm , open list , Jeffrey Hugo , Bhaumik Bhatt , Network Development Subject: Re: [RESEND PATCH v18 0/3] userspace MHI client interface driver Message-ID: References: <20210202042208.GB840@work> <20210202201008.274209f9@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <835B2E08-7B84-4A02-B82F-445467D69083@linaro.org> <20210203100508.1082f73e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210203104028.62d41962@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210209081744.43eea7b5@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210210062531.GA13668@work> <20210210104128.2166e506@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210210104128.2166e506@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed 10 Feb 12:41 CST 2021, Jakub Kicinski wrote: > On Wed, 10 Feb 2021 11:55:31 +0530 Manivannan Sadhasivam wrote: > > On Tue, Feb 09, 2021 at 08:17:44AM -0800, Jakub Kicinski wrote: > > > On Tue, 9 Feb 2021 10:20:30 +0100 Aleksander Morgado wrote: > > > > This may be a stupid suggestion, but would the integration look less a > > > > backdoor if it would have been named "mhi_wwan" and it exposed already > > > > all the AT+DIAG+QMI+MBIM+NMEA possible channels as chardevs, not just > > > > QMI? > > > > > > What's DIAG? Who's going to remember that this is a backdoor driver > > > a year from now when Qualcomm sends a one liner patches which just > > > adds a single ID to open another channel? > > > > I really appreciate your feedback on this driver eventhough I'm not > > inclined with you calling this driver a "backdoor interface". But can > > you please propose a solution on how to make this driver a good one as > > per your thoughts? > > > > I really don't know what bothers you even if the userspace tools making > > use of these chardevs are available openly (you can do the audit and see > > if anything wrong we are doing). > > What bothers me is maintaining shim drivers which just shuttle opaque > messages between user space and firmware. One of which definitely is, > and the other may well be, proprietary. This is an open source project, > users are supposed to be able to meaningfully change the behavior of > the system. > You're absolutely right in that we in general don't like shim drivers and there are several examples of proper MHI drivers - for e.g. networking, WiFi Technically we could fork/reimplement https://github.com/freedesktop/libqmi, https://github.com/andersson/diag and https://github.com/andersson/qdl in the kernel as "proper drivers" - each one exposing their own userspace ABI. But to leave these in userspace and rely on something that looks exactly like USBDEVFS seems like a much better strategy. > What bothers me is that we have 3 WWAN vendors all doing their own > thing and no common Linux API for WWAN. It may have been fine 10 years > ago, but WWAN is increasingly complex and important. > We had a deep discussion and a few prototypes for a WWAN framework going around 1-1.5 years ago. Unfortunately, what did fit Intel's view of what a WWAN device is didn't fit at all with what's run and exposed by the "modem" DSP in a Qualcomm platform. After trying to find various contrived ways to model this we gave up. > > And exposing the raw access to the > > hardware is not a new thing in kernel. There are several existing > > subsystems/drivers does this as pointed out by Bjorn. Moreover we don't > > have in-kernel APIs for the functionalities exposed by this driver and > > creating one is not feasible as explained by many. > > > > So please let us know the path forward on this series. We are open to > > any suggestions but you haven't provided one till now. > > Well. You sure know how to aggravate people. I said clearly that you > can move forward on purpose build drivers (e.g. for WWAN). There is no > way forward on this common shim driver as far as I'm concerned. But what is a WWAN device? What features does it have? What kind of APIs does it expose? Note that in this sense "QMI" really is a "binary equivalent" of AT commands, the data flows over a DMA engine, which is not part of the "WWAN device" and other services, such as GPS, already has specific transports available upstream. Regards, Bjorn