[U-Boot] [RFC PATCH 1/5] spl: dfu: add dfu support in SPL

[B, Ravi]

Hi Lukasz
 
>> >One question:
>> 
>> >Would it be possible to develop SPL (MLO) for your platform, which 
>> >does following things:
>> 
>> >1. Loads the full-fledge u-boot to SDRAM 2. Starts the u-boot and 3.
>> >u-boot flash all the needed stuff
>> 
>> >By using such approach we could restrict our dfu support in SPL 
>> >u-boot only to receiving data and uploading it to SDRAM (i.e. we 
>> >wouldn't need to add write support for ext, fat and eMMC).
>> 
>> 
>> This is not possible, because combining MLO and u-boot.img will not 
>> fit in IRAM (512k). The u-boot.img itself is around 640K.

>My point here is to first load SPL u-boot (which size is around 110 KiB), and then download via DFU full-featured u-boot, which would be placed in SDRAM.

Yes this is good idea, so the SPL-DFU will have only RAM device support (to load u-boot into DDR).
But we don't have DFU command to jump to u-boot after loading u-boot into DDR.
The DFU basically just download firmware to memory devices like mmc/sd/eMMC/RAM.
So the question is how to transfer control to u-boot after downloading the u-boot to DDR using SPL-DFU/RAM. 

>Then u-boot downloads and flash all needed images.
>One big advantage is that our SPL DFU support can be minimal - we don't need to implement fat, ext ,emmc write support.

Yes, I agree, if we could workaround above bottle neck.

Regards
Ravi