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    Subject[PATCH v2] can: j1939: do not wait 250 ms if the same addr was already claimed
    Date
    The ISO 11783-5 standard, in "4.5.2 - Address claim requirements", states:
    d) No CF shall begin, or resume, transmission on the network until 250
    ms after it has successfully claimed an address except when
    responding to a request for address-claimed.

    But "Figure 6" and "Figure 7" in "4.5.4.2 - Address-claim
    prioritization" show that the CF begins the transmission after 250 ms
    from the first AC (address-claimed) message even if it sends another AC
    message during that time window to resolve the address contention with
    another CF.

    As stated in "4.4.2.3 - Address-claimed message":
    In order to successfully claim an address, the CF sending an address
    claimed message shall not receive a contending claim from another CF
    for at least 250 ms.

    As stated in "4.4.3.2 - NAME management (NM) message":
    1) A commanding CF can
    d) request that a CF with a specified NAME transmit the address-
    claimed message with its current NAME.
    2) A target CF shall
    d) send an address-claimed message in response to a request for a
    matching NAME

    Taking the above arguments into account, the 250 ms wait is requested
    only during network initialization.

    Do not restart the timer on AC message if both the NAME and the address
    match and so if the address has already been claimed (timer has expired)
    or the AC message has been sent to resolve the contention with another
    CF (timer is still running).

    Signed-off-by: Devid Antonio Filoni <devid.filoni@egluetechnologies.com>
    ---
    v1 -> v2: Added ISO 11783-5 standard references

    net/can/j1939/address-claim.c | 40 +++++++++++++++++++++++++++++++++++
    1 file changed, 40 insertions(+)

    diff --git a/net/can/j1939/address-claim.c b/net/can/j1939/address-claim.c
    index f33c47327927..ca4ad6cdd5cb 100644
    --- a/net/can/j1939/address-claim.c
    +++ b/net/can/j1939/address-claim.c
    @@ -165,6 +165,46 @@ static void j1939_ac_process(struct j1939_priv *priv, struct sk_buff *skb)
    * leaving this function.
    */
    ecu = j1939_ecu_get_by_name_locked(priv, name);
    +
    + if (ecu && ecu->addr == skcb->addr.sa) {
    + /* The ISO 11783-5 standard, in "4.5.2 - Address claim
    + * requirements", states:
    + * d) No CF shall begin, or resume, transmission on the
    + * network until 250 ms after it has successfully claimed
    + * an address except when responding to a request for
    + * address-claimed.
    + *
    + * But "Figure 6" and "Figure 7" in "4.5.4.2 - Address-claim
    + * prioritization" show that the CF begins the transmission
    + * after 250 ms from the first AC (address-claimed) message
    + * even if it sends another AC message during that time window
    + * to resolve the address contention with another CF.
    + *
    + * As stated in "4.4.2.3 - Address-claimed message":
    + * In order to successfully claim an address, the CF sending
    + * an address claimed message shall not receive a contending
    + * claim from another CF for at least 250 ms.
    + *
    + * As stated in "4.4.3.2 - NAME management (NM) message":
    + * 1) A commanding CF can
    + * d) request that a CF with a specified NAME transmit
    + * the address-claimed message with its current NAME.
    + * 2) A target CF shall
    + * d) send an address-claimed message in response to a
    + * request for a matching NAME
    + *
    + * Taking the above arguments into account, the 250 ms wait is
    + * requested only during network initialization.
    + *
    + * Do not restart the timer on AC message if both the NAME and
    + * the address match and so if the address has already been
    + * claimed (timer has expired) or the AC message has been sent
    + * to resolve the contention with another CF (timer is still
    + * running).
    + */
    + goto out_ecu_put;
    + }
    +
    if (!ecu && j1939_address_is_unicast(skcb->addr.sa))
    ecu = j1939_ecu_create_locked(priv, name);

    --
    2.34.1
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