Recommendation for identifying partition with firmware to be loaded from SD-card

[Heinrich Schuchardt]

On 5/4/23 13:39, Michal Simek wrote:
> 
> 
> On 5/1/23 16:26, Heinrich Schuchardt wrote:
>> Linux distributions are interested in providing a single image which
>> enables a high number of boards to boot. This is simple if the boot
>> firmware (EDK II or U-Boot) is installed on flash.
>>
>> For boards that expect to load a boot loader like U-Boot from an SD-card
>> it is necessary that the firmware locations for different boards
>> on the SD-card don't collide.
>>
>> When loading from SD-card or eMMC the sector at which the binary
>> starts has to be identified. The following has been implemented:
>>
>> - start from hard coded sector number
>> - load file from FAT file system
>> - load from given partition number
>> - load from partition with boot flag set (MBR partioning only)
>> - load from partition with specific type GUID
>>
>> Loading by partition type GUID seems the most appropriate to avoid
>> collisions between the firmware for different boards.
>>
>> Often firmware is separated into multiple parts due to firmware
>> restrictions, e.g. U-Boot SPL and main U-Boot (e.g. as .itb file).
>>
>> Here the same considerations apply. Using a partition type GUID to
>> identify further firmware parts to be loaded is best suited to
>> avoid collisions.
>>
>> I would suggest to add a recommendation to the EBBR specification
>> to use SoC specific partition type GUIDs to identify firmware to
>> be loaded from SD-card.
>>
>> Please, provide your feedback.
> 
> Isn't this very similar to effort which Andre presented at Fosdem 2019?
> 
> https://archive.fosdem.org/2019/schedule/event/one_image_to_rule_them_all/attachments/slides/3342/export/events/attachments/one_image_to_rule_them_all/slides/3342/simage.pdf
> 
> Thanks,
> Michal

Thanks Michal for the pointer. We are talking about the same topic. The 
question that was not resolved up to now is how we can avoid conflicts 
between the U-Boot binaries of different SoCs stored on the same medium. 
This is where I propose to use GUID partition types.

Best regards

Heinrich