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

[Lukasz Majewski <l.majewski@samsung.com>]

Hi Ravi,

> Hi Lukasz
> 
> >> The problem here is, how o flash the images first time to fresh
> >> boards to 	QSPI or eMMC device, where there is no MMC/SD
> >> boot option available. The solution to this problem is use
> >> peripheral USB boot mode (configuring sysboot switches), where the
> >> ROM loads the intial SPL(+DFU builtin for spi/eMMC) to IRAM, then
> >> run dfu/sf or dfu/eMMC to flash the binaries from PC using USB
> >> interface. Refer to SPL-DFU support based on 2014.07 u-boot 
> >> http://www.ti.com/lit/an/sprac33/sprac33.pdf.
> 
> >I know about similar bootstrap (on TI board), which uses serial
> >instead of USB.
> 
> >In this approach MLO was loaded by serial, then it loaded u-boot,
> >which was responsible for factory setting of the device (flashing
> >rootfs, boot and other partitions).
> 
> >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.

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.

> 
> Regards
> Ravi
> 



-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group