hla: if the idcode callback returns 0, treat as a wildcard

Also document the callback accordingly.

Change-Id: I7e8ef481e8b5391b763b7f7187fac023e9fe04df
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1673
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/jtag/drivers/ti_icdi_usb.c

@@ -284,6 +284,7 @@ static int icdi_get_cmd_result(void *handle)
 
 static int icdi_usb_idcode(void *handle, uint32_t *idcode)
 {
+	*idcode = 0;
 	return ERROR_OK;
 }
 

src/jtag/hla/hla_interface.c

@@ -84,7 +84,8 @@ int hl_interface_init_target(struct target *t)
 		uint32_t expected = t->tap->expected_ids[ii];
 
 		/* treat "-expected-id 0" as a "don't-warn" wildcard */
-		if (!expected || (t->tap->idcode == expected)) {
+		if (!expected || !t->tap->idcode ||
+		    (t->tap->idcode == expected)) {
 			found = 1;
 			break;
 		}

src/jtag/hla/hla_layout.h

@@ -62,8 +62,17 @@ struct hl_layout_api_s {
 			uint32_t count, const uint8_t *buffer);
 	/** */
 	int (*write_debug_reg) (void *handle, uint32_t addr, uint32_t val);
-	/** */
-	int (*idcode) (void *fd, uint32_t *idcode);
+	/**
+	 * Read the idcode of the target connected to the adapter
+	 *
+	 * If the adapter doesn't support idcode retrieval, this callback should
+	 * store 0 to indicate a wildcard match.
+	 *
+	 * @param handle A pointer to the device-specific handle
+	 * @param idcode Storage for the detected idcode
+	 * @returns ERROR_OK on success, or an error code on failure.
+	 */
+	int (*idcode) (void *handle, uint32_t *idcode);
 	/** */
 	enum target_state (*state) (void *fd);
 };