ath79: move 8/32 boards to tiny subtarget

[Sven Roederer]

Am Sonntag, 20. September 2020, 00:21:44 CEST schrieb Adrian Schmutzler:
> > Indeed "LOW_MEMORY_FOOTPRINT" seems only to affedt 3 general options
> > and one option of OpenSSL.
> > 
> > So it might be an option to :
> > * set LOW_MEM for 8/32 MB devies
> > * set LOW_MEM and SMALL_FLASH for 4/32 MB devices
> > * check the CONFIG-options for usefull defaults So the tiny aubtarget can
> > be defined as "boards with 32MB or less of RAM; some boards also with
> > only 4MB of flash". This definition would essentially match the "4/32
> > warning" [1].
> Actually, this narrows down to a question that struck me several times
> already:
> 
> Now, that 4 MB flash devices are not "supported" anymore, how should we deal
> with the "tiny" subtargets:
> 
> 1. We keep the tiny subtargets configured for low flash, so people still
> trying to build 4 MB flash devices still can use this. (This will also
> benefit a few devices with kernel size restrictions; however, this is a
> much smaller set than in earlier times; most of these devices have
> dual-stage bootloaders now or died anyway).
> 
> 2. We convert the tiny targets to low-memory targets; this will improve the
> situation for a few devices (like you mentioned), but will make it much
> harder to still build the 4M flash devices without major changes. Apart
> from ath79, I don't know whether this would make sense for other targets
> like the old subtargets on ramips. This poses the risk of having some
> targets low-mem and some small-flash, which I'd like to avoid.
> Additionally, we will have to change back from low-mem to small-flash again
> when we start to hit limits with the 8M devices.
> 
> 3. Though not intended by this conversation, the third option is obviously
> to just ignore all 4M or 32M devices from now on (as actually announced by
> the 4/32 warning), and design the tiny targets based on the requirements of
> the 8M devices that will start to become a "problem" soon (either due to
> kernel size restrictions or because of small rootfs). Actually, we already
> went into this direction by using wpad-basic-wolfssl on tiny targets as
> well.
> 

Adrian,

thanks for reminding that 4/32 have be planned to phase out after 19.07.  This 
will or have to be done in the near future.
Reading  your points my quick idea was: "Moving the 4/32 and 8/32 to the tiny-
target for 20.xx and removing this target after 20.xx bramch-off". 
This shows clearly for 20.xx what will happen soon and the user can prepare 
for this finally. The code can possibly also cahnged to take more advantage of 
"low_mem" and "small_flash" flags for the "next 8/64 round".
regarding yout concerns that mixing 4/32 and 8/32 will make some more devices 
not usable I think like: this will break probably some 4/32 on tiny, but will 
make some 8/32 more usable. As the 4/32 warning is around fror some years now, 
nobody should be really surprised that the boards "dying" and that the 4/32 
boards dying before the 8/32.

Best Sven