[PATCH 1/2] DM_USB: allow building without OF_CONTROL

[Pali Rohár]

On Friday 25 June 2021 08:38:47 Tom Rini wrote:
> On Sun, Jun 20, 2021 at 09:43:43PM +0200, Marek Vasut wrote:
> > On 6/20/21 5:54 PM, Tom Rini wrote:
> > 
> > [...]
> > 
> > > > As far as I understand, the RX51 has gigabytes of eMMC storage, so it can
> > > > use SPL just like any other OMAP3 board.
> > > 
> > > U-Boot is being called by the old vendor X-Loader fork and needs to take
> > > up the existing flash spot.
> > 
> > So, why not place SPL in those 256 kiB and load U-Boot proper from the eMMC
> > ?
> > 
> > > > > So we need to make
> > > > > changes in subsystems they use so that they can continue to work.
> > > > > 
> > > > > So, are the changes being proposed to the generic USB code, such that
> > > > > DM_USB can be enabled, and when DM_USB_GADGET gets a deadline (Note,
> > > > > that's not set yet, but that's not to say never, it's just not been set,
> > > > > so getting ahead of problems here would be appreciated) that can also be
> > > > > enabled, OK?
> > > > 
> > > > I am confused by this reply. I noticed a lot of boards were removed over
> > > > time because they were not converted to DM/DT, and to get rid of all the
> > > > ifdefs, but now it seems the direction has been completely reversed and we
> > > > should start adding back all the ifdefs to cater for boards which are not
> > > > converted instead of fixing the boards ?
> > > 
> > > A lot of boards are being removed because no one wants to update and
> > > maintain them and they have likely not been run-time tested in years.
> > > Trying to clean up the code in those cases is best done by removing the
> > > platform, as no one using it.   That is not the case here.
> > 
> > Note that there have been boards which had to be switched to SPL to even
> > permit converting them to DM/DT, and thus prevent removal.
> > 
> > > If your only
> > > concern about the approach taken is some #ifdef's in the code, do you
> > > want to see them converted to use some wrapper macro like we do in a few
> > > other cases and __maybe_unused some functions as needed?
> > 
> > I think there is a better option which does not add any ifdefs at all _and_
> > is future-proof -- place SPL in those 256 kiB, load U-Boot from eMMC and
> > then enable all the functionality you might need in U-Boot. That would free
> > you from dealing with the size limitations basically indefinitely.
> 
> So, at this point I'm waiting for either of:
> - A response to Marek's questions about using SPL, from the Nokia NX51
>   folks.

Hello Tom! Here is my answer:

> So, why not place SPL in those 256 kiB and load U-Boot proper from the eMMC ?

U-Boot for N900 does not use SPL. There is no SPL code implemented.
Nobody ever tried to implement it and neither tested. As you have
correctly pointed instead of SPL is used vendor X-Loader binary, which
is signed by RSA key.

Add eMMC: On eMMC is stored existing operating system, which somehow
also interacts with vendor X-Loader. There was no big investigation on
this topic. Also direct booting from eMMC is not supported (unless you
crack RSA, figure out how secure things work and generate compatible
image) and neither from existing X-Loader (because vendor did not
enabled it). There is no easy access to eMMC until you start full
U-Boot. So even if all these problems are solved then "bootstrapping" or
flashing U-Boot into such location is not possible, plus there is no
recovery. Plus this loose existing and working operating system, which
is no-go. So this way is basically undebugable and therefore perfectly
hard to develop.

Not mentioning that implementing this means to implement all N900 code
in U-Boot from scratch. And the last thing is testing...

For me this idea looks like total perfectionism in corporate world when
some software architect invent a new super-duper-über solution for
everything which in reality is not possible to implement.

PS: In past few people investigated topic on cracking RSA signature on
Omap3 and nobody was able to find any "security issue" in it...

> - A patch to rework things so that USB gadget support more cleanly
>   removes from the code paths non-gadget code, so there's no #if's being
>   added here.  Or some similar clean-up.
> 
> -- 
> Tom