[PATCH] ARM: Allow MULTIPLATFORM to select XIP

On Fri, Feb 19, 2016 at 04:59:43PM +0100, Arnd Bergmann wrote:

On Friday 19 February 2016 15:36:23 Chris Brandt wrote:

quoted

On 19 Feb 2016, Arnd Bergmann wrote:

quoted

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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