There are cases where the POWER firmware must reboot in order to support specific features requested by a kernel. The kernel calls ibm,client-architecture-support and it may either return or reboot with the new feature set. eg:

Calling ibm,client-architecture-support.../
Elapsed time since release of system processors: 70959 mins 50 secs
Welcome to GRUB!

Right now we get dumped back into the grub menus and we will end up booting the default kernel the second time around if the user doesn't catch it in time.

grub2 must catch and handle this by immediately booting the same kernel again. As an example the yaboot code does this before booting a kernel:

     prom_set_options("boot-last-label", bootlastlabel,
                      strlen(bootlastlabel) + 1);

And it checks a couple of properties to see if the reboot count is above 0:

     if (prom_get_options("ibm,client-architecture-support-reboot",fw_nbr_reboots, FW_NBR_REBOOTSZ) == -1 )
        prom_get_options("ibm,fw-nbr-reboots",fw_nbr_reboots, FW_NBR_REBOOTSZ);
     fw_reboot_cnt = simple_strtol(fw_nbr_reboots,&endp,10);
     if (fw_reboot_cnt > 0L)
          prom_get_options("boot-last-label", bootlastlabel, BOOTLASTSZ);

I tested Paulo's patch and it works great. Thanks Paulo!

A simple test case for this is to boot an old kernel (I used 2.6.31) and then reboot into Fedora's latest kernel. It starts booting, then you see the client-architecture-support call and a reboot. This time grub boots directly into the latest selected kernel. Even when I edited the menu entry (for additional kernel parameters) my changes were saved and reused on the second boot.