hosted/stlinkv2: Corrected how line reset is generated for ST-Link ad…

…aptors, and switched to issuing a warning when attempting to re-select a multi-drop part

src/platforms/hosted/stlinkv2.c

@@ -502,6 +502,15 @@ int stlink_hwversion(void)
  return stlink.ver_stlink;
 }
 
+static void stlink_line_reset(void)
+{
+ stlink_simple_query(STLINK_DEBUG_COMMAND, STLINK_DEBUG_EXIT, NULL, 0);
+ uint8_t data[2];
+ stlink_simple_request(
+ STLINK_DEBUG_COMMAND, STLINK_DEBUG_APIV2_ENTER, STLINK_DEBUG_ENTER_SWD_NO_RESET, data, sizeof(data));
+ stlink_usb_error_check(data, true);
+}
+
 uint32_t stlink_adiv5_clear_error(adiv5_debug_port_s *const dp, const bool protocol_recovery)
 {
  DEBUG_PROBE("%s (protocol recovery: %s)\n", __func__, protocol_recovery ? "true" : "false");
@@ -512,9 +521,16 @@ uint32_t stlink_adiv5_clear_error(adiv5_debug_port_s *const dp, const bool proto
  * we must then re-select the target to bring the device back
  * into the expected state.
  */
- stlink_reset_adaptor();
+ stlink_line_reset();
  if (dp->version >= 2)
- adiv5_dp_write(dp, ADIV5_DP_TARGETSEL, dp->targetsel);
+ /*
+ * The correct thing to do here is some form of this:
+ * adiv5_dp_write(dp, ADIV5_DP_TARGETSEL, dp->targetsel);
+ * but ST-Link adaptors cannot handle this properly right now, so warn instead.
+ */
+ DEBUG_WARN("ST-Link v2/v3 adaptors cannot handle multi-drop correctly, pretending everything's fine\n");
+ /* Re-select the current AP on completion so we keep talking with the same thing */
+ stlink_ap_setup(stlink.apsel);
  adiv5_dp_read(dp, ADIV5_DP_DPIDR);
  }
  const uint32_t err = adiv5_dp_read(dp, ADIV5_DP_CTRLSTAT) &