The FFADO project has recently (Nov 2015) become aware that hardware changes made by Focusrite to their Saffire Pro40 interface have broken compatibility with FFADO with respect to the mixer interface (and possibly other functionality). While some users have reported streaming success, there is currently no way to control the onboard mixer or router with FFADO.
The new interfaces are still identified externally as "Pro40" which is unfortunate and will no doubt cause confusion. They do however have a different model ID (0x00de instead of 0x0005).
Several of our community members have reached out to Focusrite. Regrettably we do not have a technical contact at Focusrite who understands what we require to make the interface work under Linux, and Focusrite customer support is only willing to confirm that there have been hardware changes. Since FFADO is not receiving any vendor assistance in connection with the revised Saffire Pro40, support for the mixer and router within the new Pro40 is not possible under Linux for the foreseeable future. Such support would require a developer deduce the control protocol themselves.
As a result of these developments, FFADO recommends that Linux users avoid the revised Saffire Pro40 interface. This is disappointing given the support we have previously received from Focusrite. Note that the original Pro40 continues to work with FFADO and is a viable alternative, although as time goes on these will obviously become harder to obtain.
Whether similar revisions are planned for other Saffire interfaces remains to be seen. We suspect that if refreshed models are released for other Saffire interfaces they will have similar issues to those seen in the revised Pro40.