[ot] hw/opentitan: otp: set OTP image perms during realization

[jwnrt]

Fixes a bug where QEMU will fail to find the OTP drive on reset if the -daemonize flag is used. This flag detaches the QEMU subprocess from the current parent and changes its CWD to the root. It runs after realization and once all IOs are connected to chardevs.

If a relative path is given to -drive for the raw OTP image, it will become invalid when blk_set_perms tries to re-open the OTP image file again post-daemonization.

[AlexJones0]

This LGTM after my comments are addressed. I've walked through the issue with @jwnrt and this seems like the correct solution as far as I understand, but I'd definitely wait until @rivos-eblot or @loiclefort can check first since maybe I'm missing some understanding about the different QEMU stages.

Edit: also maybe should this be extracted to its own function to avoid cluttering _realize?

[rivos-eblot]

I need to check what if there could be any issue with multiple resets and OTP/LC update. We never used/have to use -daemonize.

I guess that this issue might also affect other devices that use the same API (flash device for example)

[jwnrt]

Yes, flash_ctrl is also running this function and re-opening the file, but it seems to be happening pre-daemonization so relative paths are okay

[rivos-eblot]

I need to check what if there could be any issue with multiple resets and OTP/LC update. We never used/have to use -daemonize.

No regression found.

[jwnrt]

Thank you for checking