Re: [linux-nfc] [PATCH 2/2] NFC: Correct outgoing frame before requeueing

[Rymarkiewicz Waldemar <waldemar.rymarkiewicz@tieto.com>]

Hi Eric,

>> BTW I see the headroom for pn544 is 2 but it make use of 1 byte (len).
>> Is that correct?
>
> That question made me go back to have a closer look. With shdlc
> currently adding the len and crc, there would be no reason for the
> driver to request any headroom. If you look at the comment above
> PN544_CMDS_HEADROOM, it says "Largest headroom needed for outgoing
> custom commands". The headroom it requests it not for len, it is used by
> the driver to insert special bytes when handling a
> pn544_hci_data_exchange for a reader F gate, which is a special case.

That makes sense. I guess in 1/2 patch PN544_CMDS_HEADROOM should be 3 
() now. Will fix that.

> I didn't remember that when I wrote the previous answer, and this
> defeats my second suggestion. I suggest we go with my first suggestion:
>
> - Specify that the driver xmit MUST NOT modify skb. It shall remove
> anything it inserts or appends before returning from xmit.

It sounds sane.

Thanks,
/Waldek