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2024-05-10 37f49e37ab4cb5d0bc4c60eb5c6d4dd57db767bb

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