# Re: \[PATCH v3 04/21\] powerpc: Return the new MSR from msr\_check\_and\_set()

- From: Michael Neuling \<hidden\>
- Date: 2016-08-19 06:47:33 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2016/08/9492209
- Thread: https://ratatoskr.run/linuxppc-dev/2016/08/9492152/t.md

```text
On Wed, 2016-08-17 at 13:43 +1000, Cyril Bur wrote:
> mfmsr() is a fairly expensive call and callers of msr_check_and_set()
> may want to make decisions bits in the MSR that it did not change but
> may not know the value of.

I can't grok this. =C2=A0Please reword.

Mikey

> This patch would avoid a two calls to mfmsr().
>=20
> Signed-off-by: Cyril Bur <redacted>
> ---
> =C2=A0arch/powerpc/include/asm/reg.h | 2 +-
> =C2=A0arch/powerpc/kernel/process.c=C2=A0=C2=A0| 4 +++-
> =C2=A02 files changed, 4 insertions(+), 2 deletions(-)
>=20
> diff --git a/arch/powerpc/include/asm/reg.h
> b/arch/powerpc/include/asm/reg.h
> index f69f40f..0a3dde9 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -1247,7 +1247,7 @@ static inline void mtmsr_isync(unsigned long val)
> =C2=A0				=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0: "memory")
> =C2=A0#endif
> =C2=A0
> -extern void msr_check_and_set(unsigned long bits);
> +extern unsigned long msr_check_and_set(unsigned long bits);
> =C2=A0extern bool strict_msr_control;
> =C2=A0extern void __msr_check_and_clear(unsigned long bits);
> =C2=A0static inline void msr_check_and_clear(unsigned long bits)
> diff --git a/arch/powerpc/kernel/process.c
> b/arch/powerpc/kernel/process.c
> index 82308fd..c42581b 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -110,7 +110,7 @@ static int __init enable_strict_msr_control(char
> *str)
> =C2=A0}
> =C2=A0early_param("ppc_strict_facility_enable", enable_strict_msr_control=
);
> =C2=A0
> -void msr_check_and_set(unsigned long bits)
> +unsigned long msr_check_and_set(unsigned long bits)
> =C2=A0{
> =C2=A0	unsigned long oldmsr =3D mfmsr();
> =C2=A0	unsigned long newmsr;
> @@ -124,6 +124,8 @@ void msr_check_and_set(unsigned long bits)
> =C2=A0
> =C2=A0	if (oldmsr !=3D newmsr)
> =C2=A0		mtmsr_isync(newmsr);
> +
> +	return newmsr;
> =C2=A0}
> =C2=A0
> =C2=A0void __msr_check_and_clear(unsigned long bits)
```