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
