Despite what is written in Radxa documentation (see Clear eMMC or SPI Flash) all my attempt to erase, read or write the SPINOR failed in maskrom mode. The eMMC as the only storage device we can work on.
It was a shame since the windows tool (RKDevTool) has the capability to select the storage device.
After looking at the RKDevTool USB transactions, I patched rkdeveloptool to gain the capability to select the storage device.
Source code is here: https://github.com/amouiche/rkdeveloptool
A pre-compiled binary here: https://github.com/amouiche/rkdeveloptool/releases/download/v1.32%2Bchange_storage/rkdeveloptool
A pull request has been submitted.
Usage example:
rkdeveloptool db rk3588_spl_loader_v1.15.113.bin
# select the SPINOR
rkdeveloptool cs 9
# clear the whole SPINOR device
rkdeveloptool ef
# write an image starting at block 0
rkdeveloptool wl 0 /tmp/spinor_image.bin