target/arm_adi_v5, cortex_m: retry ahbap_debugport_init few times in case of an error

Some targets need arbitrary amount of time (usually not too long)
after reset (both sysresetreq and srst) to do initialisation, and
SWD/JTAG is not available during that. According to PSoC4 docs, the
debugger should try connecting until it succeeds.

Also ahbap_debugport_init might be necessary to perform after using
hardware srst too, so add it there (except for the targets that
support srst_nogate since they are very unlikely to need it).

Change-Id: I3598d5ff7b8e0bf3a5566a57dec4b0b2b243d297
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2601
Tested-by: jenkins

src/target/cortex_m.c

@@ -1107,6 +1107,17 @@ static int cortex_m_deassert_reset(struct target *target)
 	/* deassert reset lines */
 	adapter_deassert_reset();
 
+	enum reset_types jtag_reset_config = jtag_get_reset_config();
+
+	if ((jtag_reset_config & RESET_HAS_SRST) &&
+	    !(jtag_reset_config & RESET_SRST_NO_GATING)) {
+		int retval = ahbap_debugport_init(target_to_cm(target)->armv7m.arm.dap);
+		if (retval != ERROR_OK) {
+			LOG_ERROR("DP initialisation failed");
+			return retval;
+		}
+	}
+
 	return ERROR_OK;
 }