I have an Acer laptop about eight years old. Its UEFI implementation leaves a bit to be desired, it implements NewxtBook but not DefaultBoot, and it resets the UEFI boot order if I change it.
The history: It started life as Win10 in a 32GB eMMC, which isn't really big enough. The laptop does have a slot for a real drive, which the advertising curiously didn't mention, so it quickly gained a 240GB SSD as well. I didn't expect to need Windows, so I clean-installed Stretch. The installer gave me the option of dual booting, so I accepted, installed Stretch on the SSD, and everything worked. Later upgraded to Buster, which killed the grub boot, it would now only cold boot to the Windows Boot Manager. After a great deal of fiddling with the /boot/efi contents, I found that NextBoot worked, so I added a Debian boot script to run efibootmgr to set it. I used the installer rescue function to boot to grub after using Windows, which was not often. Time passed, Windows outgrew its 32GB and by its nature would not put system stuff on anything but C:. It had only a few months of life left, so I clean installed Bookworm over it on the eMMC. No problems, cold booting fine, no NextBoot bodge needed. Last week I got around to upgrading to Trixie: laptop now a brick. Powering up actually gave me the blue firmware setup screens. I've had many boot failures before, going back to the days of lilo and tomsrtbt, but I've never before been kicked back to the hardware setup. The Trixie install disk got me to the reinstall grub stage, after which cold boot gave me a grub prompt. Oddly, it was grub 2.06xxx whereas when I finally got a Trixie grub menu, it's 2.12xxx. Maybe a clue? Anyway, I'm back to where I was with Buster, NextBoot will give me Trixie, but without it, a cold boot gets me that old grub prompt. So, clean installs of Stretch and Bookworm were able to boot from cold, Buster and Trixie are not. Now, I've installed grub to partition 2 of the eMMC, and the EFI stuff on partition 1, /boot/efi, is enough to boot properly if pointed to by NextBoot. There are also mmcblk0boot0 and mmcblk0boot1. These are 4MB read-only partitions, apparently in the eMMC hardware. As far as I can find out, the boot0 can be used for booting but doesn't have to be. The boot1 is a backup, which is not automatically used if boot0 is corrupted. The Acer UEFI, as I said, isn't great, and seems almost hard-wired for Windows. Is it possible this mysterious boot0 must contain something grub-related for a proper boot, which Trixie's installer isn't putting there but Bookworm's did? I gather the read-only aspect is actually imposed by Linux, and can be disabled. With the NextBoot bodge, I'm running OK, but I'd like to know what's going on, at least well enough to submit a useful bug report. I can't believe it's just a matter of luck whether Debian runs on eMMCs, of which there must be many about in cheaper computers. -- Joe
