Re: Install grub2 to ESP to boot to mmcblk0

[Pascal Hambourg]

Hello,

Le 17/09/2019 à 15:40, Toerless Eckert a écrit :
> Notebook with one nvme with EFI: ESP and vendor OS. Would like to add linux to a
> separate disk, but only option is mmcblk0 and PC bios can not boot from mmcblk0.

Is mmcblk0 an integrated eMMC module or a removable SD card ?

> Trying to add grub2 to ESP and make it boot to linux on mmcblk0, but could not
> find enough documentation how to make it work.
>
> What i tried was to install debian onto mmcblk0p1, chroot into it,
> mounted ESP onto /boot/efi, and ran grub-install --removable. This
> created grubx64.efi in ESP, but when booting to it, i only got into grub rescue.

Do you mean the ESP partition on the NVMe SSD ?

> Q: Anything that i could do in the grub rescue shell to figure out why
> its not working ? ist storage devices found or the like ?

Yes : run the command "ls" to show which drives are made available by 
the UEFI firmware. If the firmware cannot boot from mmcblk0, chances are 
that it does not even care to make it available to the boot loader. If 
it shows only one drive (hd0), then I am afraid that the only solution 
is to put the whole /boot contents in the EFI partition or any other 
location on the NVMe SSD or any other bootable device such as a USB 
drive (if acceptable).

> Q: Does grubx64.efi only rely on PC BIOS to find and read storage
> devices, or does it have the option to include its own drivers (like a
> linux kernel) to access storage type like mmcblk0 ?

By default, GRUB relies on the platform firmware but it can switch to 
native drivers with the command "nativedisk". Last time I used it with 
an ATA drive it was awfully slow. However I am not aware of a native 
SD/MMC driver. Use at your own risks.