Messages in this thread | | | Date | Tue, 18 Jun 2019 15:15:42 -0600 | From | Subash Abhinov Kasiviswanathan <> | Subject | Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver |
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On 2019-06-18 14:55, Arnd Bergmann wrote: > On Tue, Jun 18, 2019 at 10:36 PM Johannes Berg > <johannes@sipsolutions.net> 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
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