Re: RFC Need advice on reworking gpio-ep93xx.c to DT support

[Arnd Bergmann <arnd@xxxxxxxx>]

On Tue, Mar 23, 2021 at 7:57 AM Alexander Sverdlin
<alexander.sverdlin@xxxxxxxxx> wrote:
> On Mon, 2021-03-22 at 23:31 +0100, Arnd Bergmann wrote:
>
> This doesn't sound so bad as I expected. I still had no chance to figure out
> much bigger increase from 5.4 to 5.12 ;)
>
> >    text    data     bss     dec     hex filename
> > 5677321 1119704   90556 6887581 69189d build/tmp/vmlinux
> > 5782854 1143720   92188 7018762 6b190a build/tmp/vmlinux-use_of
> > 5830020 1153408   89396 7072824 6bec38 build/tmp/vmlinux-of+clk
> > 5829320 1153920   91308 7074548 6bf2f4 build/tmp/vmlinux-multi
> >
> > I also think at some point in the distant future we will require DT boot for
> > everything, but that probably comes after most ARMv4T and earlier machines
> > have fallen out of use. I'd like to get a feeling for how EP93xx fits in there,
> > can you say what memory configurations are widely deployed and how
>
> The systems I know have 32MB RAM and 16MB Flash (but only 2MB was reserved for
> compressed kernel back then).

I see, so with 32MB/2MB you are hitting both limits already and are using a
rather customized user space, and 200KB is both significant and in the
within range of the bloat you can expect from the other updates over one
or two years.

I expect the bloat problem to gradually get worse over time, as fewer
developers care about the sub-256MB machines than they used to.

On the plus side, there should be some gains in enabling
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION in the future, and
as long as we support machines without DT, you can probably add
a trivial local patch to turn off CONFIG_OF even for machines that
are multiplatform-enabled, though I would prefer not to allow that
configuration in mainline kernels.

> > long you expect them to receive kernel upgrades in the future? Are these
> > systems that will definitely get put out of use at a particular time (e.g.
> > mobile phone infrastructure for older networks or fixed-time support
> > contracts), or are these systems that you expect to keep patching until
> > the hardware dies?
>
> Yes, I expect them to work (and be patched) until they die and this
> may take another decade ;)

Ok, makes sense. I suppose once you get to the end of that time, you
can consider permanently moving to an LTS kernel, but that only gives
you two (at most six) years of updates.

       Arnd