Re: GRUB issue on device priority

[Haojian Zhuang <haojian.zhuang@linaro.org>]

On 2017/11/8 21:53, Leif Lindholm wrote:
> On Tue, Nov 07, 2017 at 10:02:30PM +0800, Haojian Zhuang wrote:
>> Hi all,
>>
>> It seems there's a device priority issue in GRUB.
> 
> GRUB is behaving as expected.
> 
>> All block io handles are linked into the list in edk2, and GRUB could fetch
>> it. Then GRUB creates its own ascending on HD priority.
>> add_device():
>>    for (p = devices; *p; p = &((*p)->next)) {
>>      ret = grub_efi_compare_device_paths (grub_efi_find_last_device_path
>> ((*p->device_path),
>>                           grub_efi_find_last_device_path->device_path));
>>      if (ret == 0) {
>>        ret = grub_efi_compare_device_paths ((*p)->device_path,
>>                                             d->device_path);
>>      }
>>      if (ret == 0) {
>>        return;
>>      } else if (ret > 0) {
>>        break;
>>      }
>>    }
>>    ...
> 
> UEFI guarantees no ordering of block devices. GRUB is a UEFI
> application, so it cannot assume anything with regards to device
> ordering.
> 
>> In the HiKey platform, I prepared the same driver for both eMMC and
>> SD. So the device paths are in below.
>> SD: /HardwareVendor(0d51905b-b77e-452a-a2c0-eca0cc8d514a)[9: 00 e0 23 f7 00 00 00 00 00 ]/UnknownMessaging(1a)/EndEntire
>> eMMC: /HardwareVendor(0d51905b-b77e-452a-a2c0-eca0cc8d514a)[9: 00 d0 23 f7 00 00 00 00 00]/UnknownMessaging(1d)/Ctrl(0)/EndEntire
>>
>> #define MSG_SD_DP                   0x1A
>> #define MSG_EMMC_DP                 0x1D
>>
>> In the second level, the device paths are different.
>>
>> And GRUB resort the sequence by ascending order (with above
>> code). So SD device always gets higher priority than eMMC device.
>>
>> If we always use installer to install OS, it may not an issue. Since
>> installer could create grub.cfg by itself. But it imports another
>> issue on lacking of persistent variable storage. And we need to
>> deploy system without installer on embedded device.
> 
> Yes, this is the bit which is interesting, and why I requested you
> post this problem to edk2-devel.
> 
> I believe that we need to have a sensible way to deal with embedded
> platforms that do not have operating systems "installed" to them, but
> rather written as images to flash devices.
> 
> So, can you clarify a few things for me?:
> - Where is GRUB located in your (pre-SD) system?

In eMMC.
> - Where is GRUB located in your SD system?
In SD.
> - Are you looking for a way to support GRUB being located on either
>    eMMC or SD? Or are you looking to always have GRUB loaded from eMMC?

GRUB could be located in either in eMMC or SD.

Best Regards
Haojian