On Wed, Aug 07, 2013 at 04:11:56PM +1000, Michael Neuling wrote:
> Add save_tar() function to save the Target Address Register (TAR). This will
> be used in a future patch to save the TAR earlier than it currently is.
>
> Signed-off-by: Michael Neuling <mi...@neuling.org>
> Cc: <sta...@vger.kernel.org>
> ---
> arch/powerpc/include/asm/switch_to.h | 5 +++++
> arch/powerpc/kernel/entry_64.S | 12 ++++++++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/switch_to.h
> b/arch/powerpc/include/asm/switch_to.h
> index 49a13e0..4531068 100644
> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -15,6 +15,11 @@ extern struct task_struct *__switch_to(struct task_struct
> *,
> struct thread_struct;
> extern struct task_struct *_switch(struct thread_struct *prev,
> struct thread_struct *next);
> +#ifdef CONFIG_PPC_BOOK3S_64
> +extern void _save_tar(struct thread_struct *prev);
> +#else
> +static inline void _save_tar(struct thread_struct *prev) {}
> +#endif
>
> extern void giveup_fpu(struct task_struct *);
> extern void load_up_fpu(void);
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 4674fe6..32e18f3 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -389,6 +389,18 @@ DSCR_DEFAULT:
> .tc dscr_default[TC],dscr_default
>
> .section ".text"
> +#ifdef CONFIG_PPC_BOOK3S_64
> +_GLOBAL(_save_tar)
> + /*
> + * Back up the TAR across context switches. Note that the TAR is not
> + * available for use in the kernel. (To provide this, the TAR should
> + * be backed up/restored on exception entry/exit instead, and be in
> + * pt_regs. FIXME, this should be in pt_regs anyway (for debug).)
> + */
> + mfspr r0,SPRN_TAR
> + std r0,THREAD_TAR(r3)
> + blr
> +#endif
Why not do this in C, as in prev->tar = mfspr(SPRN_TAR); ?
Paul.
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