On Thu, 3 Feb 2011, Tony Lindgren wrote:
> This way we can have the debug-macro.S be common for omap1 and omap2+
> and get sensible error messages booting the wrong zImage with
> CONFIG_AUTO_ZRELADDR selected. Note that this does not seem to work
> with u-boot and uImage.
>
> Signed-off-by: Tony Lindgren <[email protected]>
> ---
> arch/arm/mach-omap1/include/mach/debug-macro.S | 36
> ++++++++++++++++++++----
> arch/arm/mach-omap2/include/mach/debug-macro.S | 27 +++++++++++++++++-
> 2 files changed, 56 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/mach-omap1/include/mach/debug-macro.S
> b/arch/arm/mach-omap1/include/mach/debug-macro.S
> index 80dcf18..bae924e 100644
> --- a/arch/arm/mach-omap1/include/mach/debug-macro.S
> +++ b/arch/arm/mach-omap1/include/mach/debug-macro.S
> @@ -27,7 +27,15 @@
> .macro inituart, id, a, v
> mrc p15, 0, \a, c1, c0
> tst \a, #1 @ MMU enabled?
> +#ifdef CONFIG_AUTO_ZRELADDR
> + ldreq \a, =omap_uart_phys
> + biceq \a, \a, #0xf8000000 @ clear top bits of virt addr
> + moveq \v, pc @ copy pc
> + andeq \v, \v, #0xf8000000 @ clear lower bits
> + orreq \a, \v @ combile to get phys addr
> +#else
> ldreq \a, =omap_uart_v2p(omap_uart_phys)
> +#endif
> ldrne \a, =omap_uart_phys
Gaaaaah! This is horrible.
OK, you do want to store data in memory, right? So the best way to
always be position independent, even cross section, is to do the
following (inspired by RMK's trick in the p2v series):
.data
foo: .word 0 @ value for sput
.word 0 @ value for nik
.text
bar: .word .
.word foo
sputnik:
adr r0, bar @ get relative address of bar
ldr r1, [r0] @ get absolute address of bar
sub r1, r1, r0 @ difference between abs and rel address
ldr r0, [r0, #4] @ get absolute address of foo
sub r0, r0, r1 @ turn that into a relative address
ldmia r0, {r1, r2} @ retrieve sput and nik
add r0, r1, r2
mov pc, lr
This code is totally position independent, so it works whether or not
the MMU is active. Therefore a similar technique in your macro (you
could even put it into a macro for it) would allow you to get rid of the
mrc and test for MMU active, get rid of the #ifdef, and not be limited
to a 128 MB mask, etc. And it is just one word longer than your
shortest version i.e. 2 constants + 5 instructions vs 4 instructions + 2
literal pool entries.
Nicolas
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