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

[Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>]

Hello Arnd!

On Mon, 2021-03-22 at 23:31 +0100, Arnd Bergmann wrote:
> Unfortunately, building a multiplatform kernel makes the kernel image
> somewhat larger because it includes the code for CONFIG_OF, though
> it does not have the runtime overhead for the DT data structures that you
> get when running a DT-enabled kernel. Enabling CONFIG_USE_OF
> increased the ep93xx_defconfig build for me by 128KB, replacing
> the private clk driver with CONFIG_COMMON_CLOCK (and no driver)
> on top added another 50KB, and finally enabling multiplatform added
> another 2KB. In total, that is 2.7% total bloat in just the kernel image

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).

> 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 ;)

-- 
Alexander Sverdlin.