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

On Fri, Oct 19, 2012 at 11:30 AM, Bjørn Mork [off-list ref] wrote:

Bjørn Mork [off-list ref] writes:

quoted

Alexey Orishko [off-list ref] writes:

OK, I did some more experiments, and I am wondering if the real firmware
problem is in the MBIM descriptor.  It is

      CDC MBIM:
        bcdMBIMVersion       1.00
        wMaxControlMessage   1536
        bNumberFilters       16
        bMaxFilterSize       40
        wMaxSegmentSize      4096
        bmNetworkCapabilities 0x20
          8-byte ntb input size


so we use the 8-byte version of USB_CDC_SET_NTB_INPUT_SIZE, which fails
with -EPIPE.  But forcing the 4-byte version seems to work. Hmm, I also
see that the device returns 4 bytes in response to at
USB_CDC_GET_NTB_INPUT_SIZE with an 8-byte buffer.  Maybe we can
auto-quirk based on that?  I.e., if USB_CDC_GET_NTB_INPUT_SIZE returns
only 4 bytes then we assume that the bmNetworkCapabilities flag is
wrong.

Is that acceptable?  Then it seems we are able to inform this device of
the reduced buffer, and the other problems can be ignored.

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.

regards,
alexey
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