[U-Boot] usb flash boot on am335x machines

[U-Boot] usb flash boot on am335x machines

[matti kaasinen]

Hi!

I have tried to find solution to get am335x based Silica/Pengwyn board
booting from usb flash. U-boot on that board is based on u-boot 2013.10. I
flashed it with similar configuration as mmc flash, but I did not find
combination of configuration variables to get proper spl code generated. I
studied codes and it seemed like am33x devices were left out from usb spl
generation parts. Is there some kind of fundamental reason to prevent
am335x devices not to boot from usb flash. If not, would anyone know the
configuration combination for this set-up.

In fact, I found more than three years old patch that seems to make usb
boot set-up for am335x devices:
https://gitorious.org/rowboat/u-boot/commit/aaa9d5c083252218fd89afa68161f96bb7daa04c
However, it seems that these changed have somehow not been included in the
mainline codes. Is  there specific reason for this?

Best regards,
Matti Kaasinen

[U-Boot] usb flash boot on am335x machines

[matti kaasinen]

2015-01-26 17:46 GMT+02:00 Jon Cormier <jcormier@criticallink.com>:

> 26.1.8.6


Thanks Jon!

My interpretation from codes was pretty much what you described that USB
boot really was "modified network boot". I'm not too sure that this was HW
restriction (=CPU) but merely u-boot boot strategy decision as am335x does
have boot order strapping also for USB boot. It would be nice if I could
find clear reason why USB flash boot won't work apart from the fact that
u-boot code for am335x is not currently written in that way.

If it turns out that usb flash boot could be made possible by u-boot
patching, it would be also nice if anyone knew if this
https://gitorious.org/rowboat/u-boot/commit/aaa9d5c083252218fd89afa68161f96bb7daa04c
worked, so that I would not waste my time trying to modify them for u-boot
2013.10 if they did not work.

Thanks,
Matti

[U-Boot] usb flash boot on am335x machines

[Jon Cormier]

> Date: Mon, 26 Jan 2015 08:35:51 +0200
> From: matti kaasinen <matti.kaasinen@gmail.com>
> To: "u-boot at lists.denx.de" <u-boot@lists.denx.de>
> Subject: [U-Boot] usb flash boot on am335x machines
> Message-ID:
>         <CADnUhn33Oo-vguOFKoq0-7R0dztAohbOoCrX2qZSA9LT1SvE0w@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi!
>
> I have tried to find solution to get am335x based Silica/Pengwyn board
> booting from usb flash. U-boot on that board is based on u-boot 2013.10. I
> flashed it with similar configuration as mmc flash, but I did not find
> combination of configuration variables to get proper spl code generated. I
> studied codes and it seemed like am33x devices were left out from usb spl
> generation parts. Is there some kind of fundamental reason to prevent
> am335x devices not to boot from usb flash. If not, would anyone know the
> configuration combination for this set-up.
>
If you read the TRM carefully (26.1.8.6 USB Boot Procedure), you'll
find out that the 335x doesn't support usb flash drive boot at the
hardware level.  The USB boot option that is available creates a RNDIS
ip connection with a computer and then it does a network boot. I'll
agree that this wasn't what I was expecting when I saw USB boot.

The only way to support a USB flash boot would be if the SPL was
loaded some other means (NOR, NAND, MMC, etc) and it mounted the flash
drive and booted from it.

>
> In fact, I found more than three years old patch that seems to make usb
> boot set-up for am335x devices:
> https://gitorious.org/rowboat/u-boot/commit/aaa9d5c083252218fd89afa68161f96bb7daa04c
> However, it seems that these changed have somehow not been included in the
> mainline codes. Is  there specific reason for this?

Sorry if this doesn't correctly link to original post.  I'm unsure how
I'm supposed to reply to an email in a mailing list digest.

-- 
Jonathan Cormier
CriticalLink