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

[B, Ravi]

Hi Lukasz

>> >> Since DFU is tighly coupled to u-boot infrastructure , the size 
>> >> will increase due to multiple dependencies to compile u-boot DFU 
>> >> source in SPL. Let me re-think on possibility and come back.
>> 
>> >If you would need any assistance, please let me know (I don't have 
>> >dra7x, but I do have Beagle Bone Black).
>> 
>> The current implementation of dfu (drivers/dfu/dfu.c) relies on 
>> environment modules (getenv,setenv), and hash algo methods. The 
>> mandatory modules for DFU includes USB(dwc3/musb), gadget, 
>> drivers/dfu, hash, environ modules. Added to this mmc/sf support, with 
>> filesystem fat/ext4 would definitely increase the size.
>> 

>I've double checked BBB SPL setup:

>- SPL is the MLO (./common/spl/)
>- Its size shall be less than 128 KiB
>- It can reside on eMMC (fat partition, raw LBA offset), NAND or be sent
 > via serial port.

>I've build the am335x_boneblack_defconfig and MLO size is 75 KiB.

>Please correct me, but it seems that the SPL-DFU support adds around
>30 KiB to SPL binary size.

30KB+ is just approx size optimitzed for DFU-SF (qspi) support only, without fat/ext4, mmc support. 
But all device support may increase size.

>If yes, then even BBB's SPL can support DFU without any problems (105KiB < 128 KiB).

You mean BBB must have 128KB ? Can you confirm.
If BBB is support SPI boot, flashing MLO/U-boot to SPI-flash through SPL-DFU/SF would be sufficient right ?
Further dfu support for mmc/sd, ram available from u-boot.

>>I'm also wondering if we could even shrink the code more with reusing or extending the code at ./common/spl/spl_{ext|fat|mmc|sf, etc}.c (in this way we avoid adding the whole fat, ext, sf "commands").

Yes we must see this option. I will check on this.

>>For more aggressive size reduction we could for example disable hash algo checking and add ./common/spl/spl_dfu.c file with ordinary functions and rid of the need to add the whole dfu command.

>> I have tried minimal subset adding DFU-SF serial flash support alone 
>> in SPL, this itself increases SPL size to 30K+ (SPL size approx.
>> 107KB for dra7x). 
>> 
>> But beagle bone IRAM would be around 64KB right? Definetly this will 
>> not fit.
>> 
>> Can we enable this feature for platform with minimum SRAM size of 
>> 160KB. So SPL-DFU cannot be supported for platform less than 160KB 
>> (like am335x).

>I will ask on ML if there is any other interested party in SPL-DFU support (and what are their limitations of SPL code size).

OK.

Regards
Ravi