[U-Boot] U-Boot PXA support

[Marcel Ziswiler]

On Tue, 2019-05-21 at 14:49 +0200, Marek Vasut wrote:
> On 5/21/19 12:33 PM, Marcel Ziswiler wrote:
> > On Tue, 2019-05-21 at 12:50 +0300, Alex Sadovsky wrote:
> > > It's slightly off-topic but I wonder whether this ongoing
> > > deprecation
> > > of ARMv4 and ARMv5 (first in GCC, then in U-Boot) really
> > > simplifies
> > > anything at all.
> > > There are tons of devices that are still working good and there
> > > are
> > > even ARMv5-based MCUs that are still produced (such as CH561
> > > manufactured by WCH).
> > 
> > Please note that as of today Marvell is also still producing them
> > PXAs
> > which are not to go end-of-life before later next year I believe.
> > 
> > > IMHO it makes sense to drop only the XScale-specific tuning first
> > > and
> > > to treat PXA (and similar CPUs) as a more generic armv5te. I
> > > wonder
> > > what to do when GCC drops ARMv5 completely...
> > 
> > I believe it was only an issue with early gcc 8 but does work just
> > fine
> > again with later 8.2 or 8.3 versions.
> > 
> > However, what is more concerning to me is that in today's
> > convoluted
> > moloch known as U-Boot there may simply not be any space any more
> > for
> > something truly embedded but somewhat limited like PXA based
> > hardware.
> 
> If we ignore the PXA25x/26x, the PXA27x has loads of SRAM for U-Boot
> SPL
> and then can load U-Boot proper into DRAM. What's the problem ?

At least on the Colibri PXA270 it is more about NOR flash storage. The
factory configuration block gets stored at an offset of 0x40000 which
leaves only 256 KB for the boot loader. However, of course one could
migrate it all over to using SPL and store U-Boot proper after the
factory configuration block. But to change all that for our very oldest
module which is going end-of-live the next year may not make too much
sense.

So the real issue with U-Boot for such platforms is basically that the
complexity and footprint increased steadily leaving them behind and
eventually just removing them may be the logical conclusion. After all
we are talking about just a boot loader which is used to boot the
"real" system and good is. However, if even one percent of today's U-
Boot is actually used for booting it is probably already quite a lot
(;-p).