ath79: move 8/32 boards to tiny subtarget

[Sven Roederer]

Adrian, David,

Am Mittwoch, 16. September 2020, 16:15:42 CEST schrieb David Bauer:
> Hi,
> 
> On 9/16/20 11:40 AM, Adrian Schmutzler wrote:
> >> -----Original Message-----
> >> From: openwrt-devel [mailto:openwrt-devel-bounces at lists.openwrt.org]
> >> On Behalf Of Sven Roederer
> >> Sent: Mittwoch, 16. September 2020 09:17
> >> To: openwrt-devel at lists.openwrt.org
> >> Subject: ath79: move 8/32 boards to tiny subtarget
> >> 
> >> Hi,
> >> 
> >> not sure if this has been discussed before.
> >> I recently worked with some 8/32 boards (Ubiquiti Nanostation M (XM),
> >> TPLink
> >> WR842 v2)  for our Freifunk-project and realized that the low RAM
> >> situation
> >> requires quite different handling than the full boards (8+/64+).
> >> 
> >> I wonder if there is a reason to not move the boards, which are affected
> >> by
> >> the 4/32MB warning also, to the ath79-tiny target?
> > 
> > I wonder whether the tiny subtarget will actually make much difference for
> > RAM issues?

My idea based on the fact, to have an easy way to disable certain kernel-
features to reduce teh kernel-size (in flash and RAM). Candidates I see here 
are: USB-Support, additional filesystems, block-devices, ...
Even some devices provide USB-connectors it might be better to have less OOM-
crashes and reboots than installing a usb-flashdrive. In our Freifunk-Firmware 
I've seen much less runtime-problems with a stripped down kernel.
With having the 8/32 in tiny it would just be a config-file for the low-RAM 
boards. Having them in generic subtarget would require to build 2 kernels for 
the same subtarget.

> In it's current state, it will most likely increase low-memory issues as the
> squashfs blocksize is 1024kB compared to the regular 256kB. Not that
> ath79-tiny has no target-flag for small memory set.
> 

Did you miss an "e" ? "Note that ath79-tiny has ..." gives more sense to me. 
Reading it this way, you expect the larger blocksize was choosen as tradeoff 
between using the flash most efficient vs. RAM for the 4/32 boards?
I've seen there is a low_mem flag for some 16MB boards defined. It seems that 
for some config-options SMALL_FLASH and LOW-MEM are conflicting.

Sven