Can the HOLD# and WP# pins be connected directly to VCC on the S25FL-S and S25FL-L Serial Flash devices without causing a problem?
Yes, if you don’t need the HOLD# and WP# functions and if you are using single-IO or dual-IO, these pins can be connected directly to VCC or VIH. However, both pins can also be left unconnected since each has an internal pull-up. There are special cases, though, to be aware of.
If you are using quad-IO, these pins are multiplexed with IO2 and IO3, both of which are needed to support the quad-IO function. In other words, if the QUAD bit is set to enable the quad-IO function, then these pins represent IO2 and IO3, which must be connected to your SPI controller.
FL-S is the simpler case in that a single bit – the Configuration Register 1 setting CR1 = QUAD – controls which of the multiplexed cases apply to IO2/WP# and IO3/HOLD#. From the FL-S datasheet (document 001-98292 Rev J):
The FL-L is more complicated in that either quad-IO mode or QPI (4-4-4) mode require full access to IO2 and IO3. As always, study the datasheet to learn the details. For reference, here is the signal description for the FL-L (document 002-00124 Rev C):