[PATCH] ARM: Allow MULTIPLATFORM to select XIP

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Fri, Feb 19, 2016 at 04:59:43PM +0100, Arnd Bergmann wrote:
> On Friday 19 February 2016 15:36:23 Chris Brandt wrote:
> > On 19 Feb 2016, Arnd Bergmann wrote:
> > 
> > > For PHYS_OFFSET, parsing the DT doesn't help at all because we only
> > > need it for XIP_KERNEL (more or less at least) which cannot patch
> > > the kernel image at boot time, so knowing that the address is wrong
> > > also doesn't help you.
> > > 
> > > 	Arnd
> > 
> > OK, at first I was thinking that PHYS_OFFSET was only used early in boot as a pointer to valid RAM before the DT was read (in head.S and head-nommu.S). Hence, you could pass in the pointer in via another CPU register like the DT pointer is passed in.
> > 
> > But, now I see that PHYS_OFFSET is used all over the place as a hard coded #define, hence your comment "which cannot patch the kernel image at boot time"
> > 
> > So, I retract my thought...it has to be configured at build-time (unless of course you turn it into a global variable everywhere...which might be an even bigger mess)
> > 
> 
> BTW, I've tried removing the patching in CONFIG_PHYS_VIRT and replaced it
> with references to __pv_phys_pfn_offset, which surprisingly only grew
> .text from 4901692 to 4904300 bytes, so the size overhead of doing this
> would be close to zero.

The next job is to perf the resulting kernel - because you will have
the additional overhead of loading the offset.  Size is not everything,
contary to popular beliefs.

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