Re: [PATCH net-next 02/14] net: cdc_ncm: use device rx_max value if update failed

Alexey Orishko [off-list ref] writes:

Based on NCM errata, NCM functional descriptor: if Bit 5 is set, then
device can (must) handle 8-byte form of Set/GetNtbInputSize.
If they set a flag, but don't support the feature, hm.. is it a
prototype device or
commercially available one?

At least device must support Set request, but for GetNtbInputSize we
could happily
live without wNtbInMaxDatagrams (i.e. use 4 byte variant) on Linux.
Since we must anyway receive a complete NTB and making any number of skb
buffers from received NTB is not a problem at all.

OK, I may have misunderstood you here.  Quoting the errata text:

<quote>
  If bit D5 is set in the bmNetworkCapabilities field of function’s NCM
  Functional Descriptor, the host may set wLength either to 4 or to
  8. If wLength is 4, the function shall assume that wNtbInMaxDatagrams
  is to be set to zero. If wLength is 8, then the function shall use the
  provided value as the limit. The function shall return an error
  response (a STALL PID) if wLength is set to any other value.
</quote>

So the 4 byte variant is always supported and we might as well just use
it unconditionally because we don't set, or need to set, the
wNtbInMaxDatagrams.

Is that right?  It will simplify the code even more without any loss of
functionality, except for the possibility of failing on some other buggy
device not supporting the 4 byte variant...


Bjørn
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