[U-Boot] SPL Dfu update

[Tom Rini]

On Wed, Oct 30, 2013 at 09:11:43PM +0100, Wolfgang Denk wrote:
> Dear Michael Trimarchi,
> 
> In message <CAOf5uw=hCkwPaqogCO3KvM1erhS-dvC5BRT4USU3uqKETtTQ7A at mail.gmail.com> you wrote:
> > 
> > > This does not answer Stefano's question: why do it in SPL, what's
> > > wrong with loading the real U-Boot for this purpose?
> > 
> > Because it's not possible, internal memory size of some cpus. You need
> > to have a way to load the second stage and I'm discussing a general
> > way to do.
> 
> I'm not sure that there are many use cases where you have sufficient
> room for all that is needed for DFU (including I/O buffers); and if
> you move to RAM early, you have other options as well.

No, it's true.  We have some "small" amount of image download area in
some sort of on-chip RAM (OMAP3 is between 54 and 62KiB, depending on
how we think about stack, AM335x is ~110KiB) which is where our first
stage _has_to_ fit.  We can still do a two-step process here of loading
a regular SPL and then a full U-Boot, but this requires more complicated
host side tooling.

But this is what I was trying to highlight, about how Scott's comment is
right.  What's desired here, rightly is a U-Boot build with limited IO
and a main loop that drops right into DFU.  You can do this today with
SPL+U-Boot and a CONFIG_BOOTCOMMAND that just kicks off DFU.  But that
means transferring more data, which is taking more time and yes,
programming time is a concern.

> > What is your alternative way?
> 
> Depending on your hardware there is a zillion ways to do this.  For
> low to medium volumes good old JTAG is still a very powerful tool; for
> high volumes you will probably just fit pre-programmed NAND on your
> board.  And of course there is the growing number of systems that can
> just boot and install from a SDCard or USB MSD.

Exactly.  But you're leaving out "system boots via USB gadget", which is
what Michael is trying to solve.

-- 
Tom
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