Re: [PATCH 1/6] Add infrastructure for conditional code and data sections

[Tony Lindgren <tony@atomide.com>]

* Thomas Petazzoni <thomas.petazzoni@free-electrons.com> [101221 10:20]:
> From: Thomas Petazzoni <tpetazzoni@ti.com>
> 
> WARNING: This is only a proof-of-concept, there are many known
> issues. The sole purpose of this patch is to get some feedback on
> whether the idea is useful or not, and whether it's worth cleaning up
> the remaining issues.
> 
> A trend in the kernel support for SoC is to build a single kernel that
> works accross a wide range of SoC inside a SoC family, or even in the
> future SoC of different families.
> 
> While this is very interesting to reduce the number of kernel images
> needed to support a large number of hardware platforms, it allows
> means that the kernel image size is increasing. Portions of code and
> data are specific to a given SoC (clock structures, hwmod structures
> on OMAP, etc.) and only the portion relevant for the current SoC the
> kernel is running on is actually useful. The rest of the code and data
> remains in memory forever.
> 
> While __init and __initdata can solve some of those cases, it is not
> necessarly easy to use, since the code/data that is actually useful
> needs to be copied so that it is kept after the init memory cleanup.
> 
> Therefore, we introduce an infrastructure that allows to put code and
> data into specific sections, called "conditional sections". All those
> sections are compiled into the final kernel image, but at runtime, by
> calling a function, we can get rid of the unused sections.

Great, something is certainly needed to free the unused memory.
 
> For example, on OMAP, you can declare data as being omap2 specific
> this way:
> 
>    static int __omap2_data foobar;
> 
> Then, in the board code of an OMAP3 or OMAP4 platform, you can call:
> 
>    free_unused_cond_section("omap2");

Sounds like this could be done after the cpu detection automatically?

I don't know what the section limitations are, but it would be nice
to have a separate section for each machine.. Then we could just
"free_unused_machines()" during the init.. :)

Tony