How chip makers should (not) support Free Software

Silicon manufacturers, or rather design houses play a key aspect in how well
their products are supported in Free Software oparating systems such as Linux.
In the early Linux days  - more than a decade ago - it was normal to have
completely public technical reference manuals for the silicon, enabling Linux
community developers to write drivers for the chips.
After chip design houses start to realize there is an economically significant
Linux market, they try to use their existing workflow, processes and
development model for proprietary operating systems and try to apply this to
Linux.  The result are in many cases binary-only drivers for certain Kernel
versions and/or distributions or unmaintained, non-portable, coding style
incompliant open source drivers for outdated kernel versions.  Those kind of
drivers are bound to create dissatisfaction within the Free Software developer
community, among the Free Software users.  Furthermore, they also result in
inefficient use of R&D resources both inside and outside the chip vendor.

Many silicon design houses still don't understand the Free Software and
particularly Linux development model at all.  This results in suboptimal
support of their hardware products.  In the end, customers are likely to buy
from a different vendor.

So what can chip design houses do to ensure excellent support of their products
in the Free Software world?