Oh dear, this one is causing me some trouble!
I still cannot get my MIMXRT1021 QSPI to boot using the secondary pinmux configuration, but I think I understand why....I just don't know how to fix it.
I have BOOT_CFG[3:1]=111b and it is indeed going to the secondary chip at around 30MHz clock, selecting it, writing a read request and waiting for data to come back....trouble is, the data never comes back. The reason for that is that /HOLD (IO3) is low - so as far as the flash is concerned it isn't supposed to respond. When I look on the 1021EVK (which uses the primary pinmux) /HOLD is high, and the flash reads out correctly. In all other respects the signals appear identical.
I have placed external (5K6) pullups on D0..D3 and now I can at least get the processor to read something from the flash, and it responds to erase requests correctly. I didn't see anything about needing external pullups in either the Technical Datasheet or the User Manual, and I can't yet write to the flash properly.
Is there any additional data about using the secondary/alternate pinmux or a bit of guidance? Can't help feeling I'm flying a bit blind here...