After updating to -current and 3.7.1, my LUKS prompt no longer works with my USB keyboard. I did the usual mkinitrd:

I have to switch to PS/2 in order to enter the LUKS password. After that, I can switch back to USB and continue as usual, so it just appears to be the LUKS prompt that has the problem.

I tried changing uhci-hcd to ehci-hcd (actually, I added them both), thinking that the kernel now uses EHCI instead of UHCI, but it made no difference. I can see all the modules being loaded just before it shows the prompt. I’ve not had this problem using previous kernels with that mkinitrd command.

Edit: It’s probably worth noting that I ran out of disk space when doing the upgrade, but I “slackpkg reinstall kernel”’d after clearing space and the upgrade continued without any further problem.

Check you didn't make the same typo in your initrd module list that you have above. It should be 'ehci-hcd'. not 'ehci-hid'. Other than that, you're thinking pretty much along the same lines and doing exactly what I would have.
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Just a typo in the post. I’ll correct it.

Yep, no worries. I thought it might be but it was worth ruling out.

I found that I have to add hid-generic:

This is probably due to the later kernels, and should be added to README_CRYPT.TXT in the "USB keyboards and LUKS" section.

Posted on wrong thread..ignore