Hi kenshow,
You can find more information about port writes in the Error Managment Spec (Part 8) of RapidIO. Taking a look at the following post should provide some insight as well. Specifically, it details how to disable port writes.
http://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/439/p/262359/918548.aspx#918548
Were you encountering any issues because of this bit being set?
Thanks,
Clinton