netdev - Re: Is this 32-bit NCM?

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Date:	Thu, 27 Nov 2014 11:03:24 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Enrico Mioso <mrkiko.rs@...il.com>
Cc:	youtux@...il.com, alexxst@...il.com, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: Is this 32-bit NCM?

Enrico Mioso <mrkiko.rs@...il.com> writes:

> Ok - we can arrive to some ocnclusions regarding the E3272.
> First of all - the modem seems buggy enough to not be able to handle requests 
> for different formats. You need to unplug and re-plug it, but this is onlyan 
> impression and is reasonable.
>
> Then - the modem will accept to ndisdup the connection with
> at^ndisdup=1,1,"internet"
> but - if we use huawei_cdc_ncm + cdc_ncm we have no flow handling messages and 
> the modem stops here.
> If we use the cdc_ncm 32-bit driver (modified) we get lotfs of
> ^dsflorpt
> that's how it should be.
> So I think we can say that something is changing.
> Then there's the alignment problem you mentioned in your previous reply. And 
> this is hard to solve.
> could you try to help me understand where the problem is?
> I feel like we are very close to the solution but something isn't working.
> Or might be just try to change the 16 bit driver?

If you use a recent version of the driver as a basis, then you get the
CDC NCM NTB parameters in sysfs (if not, then you need to enable
debugging and look in the log for these values).  For example:

bjorn@...i:~$ grep . /sys/class/net/wwan0/cdc_ncm/*
/sys/class/net/wwan0/cdc_ncm/bmNtbFormatsSupported:0x0001
/sys/class/net/wwan0/cdc_ncm/dwNtbInMaxSize:15360
/sys/class/net/wwan0/cdc_ncm/dwNtbOutMaxSize:15360
/sys/class/net/wwan0/cdc_ncm/min_tx_pkt:13824
/sys/class/net/wwan0/cdc_ncm/rx_max:15360
/sys/class/net/wwan0/cdc_ncm/tx_max:15360
/sys/class/net/wwan0/cdc_ncm/tx_timer_usecs:400
/sys/class/net/wwan0/cdc_ncm/wNdpInAlignment:4
/sys/class/net/wwan0/cdc_ncm/wNdpInDivisor:1
/sys/class/net/wwan0/cdc_ncm/wNdpInPayloadRemainder:0
/sys/class/net/wwan0/cdc_ncm/wNdpOutAlignment:4
/sys/class/net/wwan0/cdc_ncm/wNdpOutDivisor:32
/sys/class/net/wwan0/cdc_ncm/wNdpOutPayloadRemainder:0
/sys/class/net/wwan0/cdc_ncm/wNtbOutMaxDatagrams:32

The possible problem I am thinking of is proper handling of the
wNdp*PayloadRemainder values. See section 3.3.4 "NCM Ethernet Frame
Alignment" in the spec.  Which is confusing as hell, but if I understand
it correctly then we are supposed to align the start of the IP packets
(the "payload", _not_ the ethernet frame) to a whole wNdp*Divisor number
as long as the wNdp*PayloadRemainder is 0.

Bjørn
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