[bootwrapper PATCH 05/13] aarch64: add mov_64 macro

[Andre Przywara]

On Wed, 12 Jan 2022 14:18:52 +0000
Mark Rutland <mark.rutland at arm.com> wrote:

> On Tue, Jan 11, 2022 at 02:41:49PM +0000, Andre Przywara wrote:
> > On Tue, 11 Jan 2022 13:06:45 +0000
> > Mark Rutland <mark.rutland at arm.com> wrote:
> > 
> > Hi,
> >   
> > > In subsequent patches we'll need to load 64-bit values into GPRs before
> > > the CPU is in a known endianness, where we cannot use literal pools.
> > > 
> > > In preparation for that, this patch adds a new `mov_64` macro to load a
> > > 64-bit value into a GPR using a sequence of MOV and MOVKs, which will
> > > function the same regardless of the CPU's endianness.
> > > 
> > > At the same time, move the `cpuid` macro to use `mov_64` internally.
> > > 
> > > Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> > > ---
> > >  arch/aarch64/common.S | 10 +++++++++-
> > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/aarch64/common.S b/arch/aarch64/common.S
> > > index c7171a9..3279fa9 100644
> > > --- a/arch/aarch64/common.S
> > > +++ b/arch/aarch64/common.S
> > > @@ -9,9 +9,17 @@
> > >  
> > >  #include <cpu.h>
> > >  
> > > +	/* Load a 64-bit value using immediates */
> > > +	.macro	mov_64 dest, val
> > > +	mov	\dest, #(((\val) >>  0) & 0xffff)
> > > +	movk	\dest, #(((\val) >> 16) & 0xffff), lsl #16
> > > +	movk	\dest, #(((\val) >> 32) & 0xffff), lsl #32
> > > +	movk	\dest, #(((\val) >> 48) & 0xffff), lsl #48
> > > +	.endm
> > > +  
> > 
> > Trusted Firmware has an (admittedly more complicated) version that only
> > uses as many instructions as needed, by skipping over halfwords that are
> > zero:
> > https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/include/arch/aarch64/asm_macros.S#n125
> > 
> > Does that sound useful for us?  
> 
> For simplicity/clarity, I'd prefer to keep this as-is.
> 
> That and I'm not entirely sure about how the boot-wrapper and TF-A licenses
> interact, so generally I'd strongly prefer to avoid importing code.

Fair enough, I just found the functionality of that TF-A version
particularly neat, though indeed somewhat hard to understand and possibly
over-engineered for us.

Cheers,
Andre

> >   
> > >  	/* Put MPIDR into \dest, clobber \tmp and flags */
> > >  	.macro cpuid dest, tmp
> > >  	mrs	\dest, mpidr_el1
> > > -	ldr	\tmp, =MPIDR_ID_BITS
> > > +	mov_64	\tmp, MPIDR_ID_BITS
> > >  	ands	\dest, \dest, \tmp
> > >  	.endm  
> >