[RFC PATCH v3] ARM: Introduce patching of phys_to_virt and vice versa
Russell King - ARM Linux
linux at arm.linux.org.uk
Wed Nov 10 15:37:44 EST 2010
On Wed, Nov 10, 2010 at 03:23:50PM -0500, Nicolas Pitre wrote:
> > add rd, rn, #PHYS_OFFSET - PAGE_OFFSET
> > and phys_to_virt() is:
> > sub rd, rn, #PHYS_OFFSET - PAGE_OFFSET
> Does this work even if PHYS_OFFSET - PAGE_OFFSET goes negative?
add rd, rn, #0xc0000000
sub rd, rn, #0x40000000
are identical operations. The operand is an 8 bit constant, zero padded,
rotated right by (in this case) 8 bits - there can be no sign extension.
> On Wed, 10 Nov 2010, Russell King - ARM Linux wrote:
> > Here's something which uses the above ideas (untested). I think this is
> > something we can (and should) do unconditionally for the !XIP cases.
> What do you mean by "unconditionally"?
For any machine where the v:p offset is respresentable. It means that
we increase the amount of testing, and actually this becomes the
> > +2: cmp r4, r5
> > + ldrlo r7, [r4], #4
> > + ldrlo ip, [r7, r3]
> > + bic ip, ip, #0x000000ff
> > + bic ip, ip, #0x00000f00
> > + orr ip, ip, r6
> The above 3 insns could be replaced with:
> mov ip, ip, lsr #12
> orr ip, r6, ip, lsl #12
They could be, but it's not worth optimizing to that extent - we're
already hitting load delays for both of those ldr instructions that
this isn't going to be blindingly fast... at least there aren't
thousands of them to fixup.
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