[U-Boot] Dumb question: is UMS/MASS_STORAGE_GADGET in SPL possible?

[Lukasz Majewski <lukma@denx.de>]

Hi Jason

> I'm trying to make a small image enabling u-boot UMS mode on
> BeagleBone Black against the on-board eMMC. Is it possible to enable
> UMS simply within SPL?

As fair as I remember UMS is not supported in SPL.

However, recently there was an attempt to use the DFU gadget in SPL
(CONFIG_SPL_DFU_RAM):

http://u-boot.10912.n7.nabble.com/RFC-PATCH-v3-0-5-SPL-DFU-Support-in-SPL-td262621.html#a262626

It is already supported in ML. You can look into this implementation
and add similar code to support UMS.

> 
> It seems like some others have done it in the past (
> http://lists.denx.de/pipermail/u-boot/2015-March/207600.html), but I
> don't see an obvious way to enable it.

In the link the UMS support is disabled to avoid too big size grown.

> 
> Performance might not be great (
> https://boundarydevices.com/u-boot-usb-mass-storage-gadget/), but
> minimizing the user steps could make it worth doing it in u-boot
> (preferably SPL) than to load a kernel and ramdisk (
> https://github.com/ungureanuvladvictor/BBBlfs).

Maybe you can reuse as much as possible from the SPL-DFU support?

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Best regards,

Lukasz Majewski

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