Hi Waldek, On 09/07/2012 08:38 AM, Rymarkiewicz Waldemar wrote: > Hi Eric, > >> This patch would work for PN544, but it makes the assumption that the >> driver will always insert/append exactly client_headroom/client_tailroom >> bytes when xmit is called. This is not specified nor enforced so it may >> be a little dangerous. > > Do you mean that the driver can request client_head/tailroom which is a > maximum it can use, but it does not mean that all space will be used in > in each frame e.g. due to optional fields? That's the only situation I > can imagine now. Yes, this is exactly what I mean. > 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. 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. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
