Re: [PATCH] setup.c: introduce __pa_symbol() and get ride of CPHYSADDR()

[Thiemo Seufer <ths@networkno.de>]

Franck Bui-Huu wrote:
[snip]
> >> If so could you explain the choice of these values
> >> because I fail to understand it.
> > 
> > It allows to load a 64-bit kernel in KSEG0,
> 
> sorry to be ignorant of 64 bit kernels, but what's the point
> to load them in KSEG0.

Smaller code with better performance.

> > and use short 2-instruction symbol references there.
> 
> do you mean "it allows to use only 2 'lui' instructions to load
> a symbol address into a register" ?

It allows a 2-instruction "lui ; addiu" sequence instead of a
6-instruction "lui ; lui ; addiu ; addiu ; dsll32 ; addu" sequence.

> Futhermore I don't see how some part of the kernel convert virtual
> address into a physical one with such values. For example in setup.c,
> the function resource_init() does:
> 
> 	code_resource.start = virt_to_phys(&_text);
> 	code_resource.end = virt_to_phys(&_etext) - 1;
> 	data_resource.start = virt_to_phys(&_etext);
> 	data_resource.end = virt_to_phys(&_edata) - 1;
> 
> How does it work in this case ?

Those are addresses in 64-bit space, no special handling is needed
there.

The same doesn't hold for the initrd addresses supplied by the (32-bit)
firmware. The firmware doesn't convert the kernel parameters to 64-bit
values because the O2 kernel used to allow a pure 32-bit build, and the
firmware can't find out what's actually inside the object file.


Thiemo