On Fri, 2019-05-31 at 17:59 -0600, Subash Abhinov Kasiviswanathan wrote: > On 2019-05-31 17:33, Bjorn Andersson wrote: > > On Fri 31 May 13:47 PDT 2019, Alex Elder wrote: > > > > > On 5/31/19 2:19 PM, Arnd Bergmann wrote: > > > > On Fri, May 31, 2019 at 6:36 PM Alex Elder <elder@xxxxxxxxxx> > > > > wrote: > > > > > On 5/31/19 9:58 AM, Dan Williams wrote: > > > > > > On Thu, 2019-05-30 at 22:53 -0500, Alex Elder wrote: > > > > > > > > > > > > My question from the Nov 2018 IPA rmnet driver still > > > > > > stands; how does > > > > > > this relate to net/ethernet/qualcomm/rmnet/ if at all? And > > > > > > if this is > > > > > > really just a netdev talking to the IPA itself and > > > > > > unrelated to > > > > > > net/ethernet/qualcomm/rmnet, let's call it "ipa%d" and stop > > > > > > cargo- > > > > > > culting rmnet around just because it happens to be a net > > > > > > driver for a > > > > > > QC SoC. > > > > > > > > > > First, the relationship between the IPA driver and the rmnet > > > > > driver > > > > > is that the IPA driver is assumed to sit between the rmnet > > > > > driver > > > > > and the hardware. > > > > > > > > Does this mean that IPA can only be used to back rmnet, and > > > > rmnet > > > > can only be used on top of IPA, or can or both of them be > > > > combined > > > > with another driver to talk to instead? > > > > > > No it does not mean that. > > > > > > As I understand it, one reason for the rmnet layer was to > > > abstract > > > the back end, which would allow using a modem, or using something > > > else (a LAN?), without exposing certain details of the hardware. > > > (Perhaps to support multiplexing, etc. without duplicating that > > > logic in two "back-end" drivers?) > > > > > > To be perfectly honest, at first I thought having IPA use rmnet > > > was a cargo cult thing like Dan suggested, because I didn't see > > > the benefit. I now see why one would use that pass-through layer > > > to handle the QMAP features. > > > > > > But back to your question. The other thing is that I see no > > > reason the IPA couldn't present a "normal" (non QMAP) interface > > > for a modem. It's something I'd really like to be able to do, > > > but I can't do it without having the modem firmware change its > > > configuration for these endpoints. My access to the people who > > > implement the modem firmware has been very limited (something > > > I hope to improve), and unless and until I can get corresponding > > > changes on the modem side to implement connections that don't > > > use QMAP, I can't implement such a thing. > > > > > > > But any such changes would either be years into the future or for > > specific devices and as such not applicable to any/most of devices > > on > > the market now or in the coming years. > > > > > > But as Arnd points out, if the software split between IPA and rmnet > > is > > suboptimal your are encouraged to fix that. > > > > Regards, > > Bjorn > > The split rmnet design was chosen because we could place rmnet > over any transport - IPA, PCIe (https://lkml.org/lkml/2018/4/26/1159) > or USB. Yeah, that's what I was looking for clarification on :) Clearly since rmnet can have many transports it should be able to be used by different HW drivers, be that qmi_wwan, IPA, and maybe even rmnet_smd.c? > rmnet registers a rx handler, so the rmnet packet processing itself > happens in the same softirq when packets are queued to network stack > by IPA. This directly relates to the discussion about a WWAN subsystem that Johannes Berg started a couple weeks ago. IPA appears to create a netdev of its own. Is that netdev usable immediately, or does one need to create an rmnet device on top to access the default PDN? Thanks, Dan
