In general, the variables in the 18 structure are not used
until after the 19 function (see section #secdetect#1266>) is
called. Therefore, any variables which cannot be assigned before host
adapter detection should be assigned during detection. This situation
might occur, for example, if a single driver provided support for several
host adapters with very similar characteristics. Some of the parameters in
the 20 structure might then depend on the specific host
adapter detected.