[U-Boot] [RFC PATCH v2 4/5] dra7x: boot: add dfu bootmode support

[B, Ravi]

Hi Tom

>> 
>> You are correct. This platform does not support BOOT_DEVICE_USB support.
>> The BOOT_DEVICE_USB is basically the USBHOST-MSC support (CONFIG_SPL_USB_SUPPORT), i.e, boot from mass storage device.

>So, we have 3 SoCs that share these values here, and we need to be correct for all of them.  What does 0x45 mean, on OMAP5, DRA7xx and AM57xx, in terms of what, and how, the ROM loaded something in?

For all  OMAP5/DRA7X/AM57X  devices, 0x45 means ROM-USB peripheral boot mode. You are correct, as pointed out, the "ROM enumerated as USB gadget (type : vendor specific download gadget)".

>> Yes, this platform don't have USBHOST-MSC support, hence BOOT_DEVICE_USB is not valid for this device and removed, and also does not support BOOT_DEVICE_USBETH as well.

>When you say platform and device, do you mean SoC, or the specific EVM you're working with?

>> Instead BOOT_DEVICE_DFU  is defined for USB-Gadget-DFU support, i.e, boot from USB-DFU.

>It sounds like you're saying here that 0x45, for DRA7xx/AM57xx means "ROM enumerated a USB gadget (of type what?) and was given a payload".

Correct. ROM implements custom download gadget.

>This is what, on TI platforms, usually happens with 0x45.  Sometimes it's a USB RNDIS device and bootp (am33xx, am43xx), sometimes it's a something else 

Yes you are correct, there is only one USB mode implemented in ROM (either host boot  or peripheral boot mode).

 >(I honestly forget what OMAP4 did, I think it was just a vendor class self-defined and spec-allowed thing).  What is happening in this case, and how do we get this first part in?

I am not sure on OMAP4, it must be similar to OMAP5 which is vendor class specific download gadget.

Regards
Ravi