Re: [Minios-devel] [UNIKRAFT PATCHv6 11/37] plat/common: Introduce SYSREG_READ32/64 SYSTEM_WRITE32/64 for different size

[Julien Grall <julien.grall@xxxxxxx>]

On 09/17/2018 08:18 AM, Wei Chen (Arm Technology China) wrote:
> Hi Julien,
Hi,

> > -----Original Message-----
> > From: Julien Grall <julien.grall@xxxxxxx>
> > Sent: 2018年9月17日 8:44
> > To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> > devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> > Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv6 11/37] plat/common: Introduce
> > SYSREG_READ32/64 SYSTEM_WRITE32/64 for different size
> >
> > Hi,
> >
> > On 09/14/2018 08:56 AM, Wei Chen wrote:
> > > On Arm, the system registers may have different size. Introduce these
> > > four helpers will give us a direct visual about the register's size we
> > > are accessing.
> > >
> > > Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> > > ---
> > >    plat/common/include/arm/arm64/cpu.h | 14 ++++++++++++++
> > >    1 file changed, 14 insertions(+)
> > >
> > > diff --git a/plat/common/include/arm/arm64/cpu.h
> > b/plat/common/include/arm/arm64/cpu.h
> > > index 702761c..db8be9c 100644
> > > --- a/plat/common/include/arm/arm64/cpu.h
> > > +++ b/plat/common/include/arm/arm64/cpu.h
> > > @@ -90,3 +90,17 @@ static inline void ioreg_write64(volatile uint64_t *addr,
> > uint64_t value)
> > >    #define SYSREG_WRITE(reg, val) \
> > >         __asm__ __volatile__("msr " __STRINGIFY(reg) ", %0" \
> > >                         : : "r" ((uint64_t)(val)))
> > > +
> > > +#define SYSREG_READ32(reg) \
> > > +({     uint32_t val; \
> > > +       __asm__ __volatile__("mrs %0, " __STRINGIFY(reg) \
> > > +                       : "=&r" (val)); \
> > I am not entirely sure why you need the earlycloberr (&) here. The
> > operand will not be written before the instruction has finished.
> Is there any harm that I am using the "&", because I always use it
> in such case?
My point here is you add & which does not make sense in the current 
context. Can you explain why you always put it in such case?
Cheers,

--
Julien Grall

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