Hints on how to use efi_driver/efi_block_device.c

[Heinrich Schuchardt]

On 8/12/21 11:49 PM, Simon Glass wrote:
> +Heinrich Schuchardt too
>
> On Thu, 12 Aug 2021 at 08:35, Christian Melki
> <christian.melki at t2data.com> wrote:
>>
>> I was hoping that U-boot would detect BLOCK_IO devices provided by UEFI
>> automatically. But I can't see anything attached under lsblk or find
>> some other information about this.
>> For example, Barebox works just fine on both Virtualbox and real
>> hardware in this regard.
>>
>> Barebox does not have an emmc driver for the real hardware but
>> piggybacks off the UEFI protocol for this.

Hello Christian,

U-Boot can be used in two scenarios:

1) U-Boot is the firmware providing the UEFI API
2) U-Boot is running as an application consuming the UEFI API.

Barebox only supports scenario 2).

>>
>> I'm sure that the idea with this U-boot driver is something like that,
>> but would appreciate some hints on how to use it.

efi_driver/efi_block_device.c is used in scenario 1).

When a UEFI payload like iPXE provides an EFI_BLOCK_IO_PROTOCOL on a
handle and calls ConnectController() U-Boot will install the
EFI_SIMPLE_FILE_PROTOCOL for each partition on the block device.

You can find a detailed description of this use case in:

* https://u-boot.readthedocs.io/en/latest/develop/uefi/iscsi.html
* https://archive.fosdem.org/2020/schedule/event/firmware_duwu/

>>
>> Ie, standard usage. UEFI boots of a drive, posts some handles(?) to a
>> block device and U-boot picks it up, not knowing more about the
>> abstracted hardware.

Here you seem be referring to scenario 2).

For scenario 2) support for UEFI block devices has not been implemented,
yet. As operating systems like Linux, BSD, Windows all can be booted via
UEFI there has not been any use case driving further development of this
scenario.

Please, describe what you want to do with U-Boot.

Best regards

Heinrich