Patchwork [2/4] powerpc: Add new save_tar() register function.

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Submitter Michael Neuling
Date Aug. 7, 2013, 6:11 a.m.
Message ID <1375855918-3625-2-git-send-email-mikey@neuling.org>
Download mbox | patch
Permalink /patch/265334/
State Superseded
Headers show

Comments

Michael Neuling - Aug. 7, 2013, 6:11 a.m.
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 <mikey@neuling.org>
Cc: <stable@vger.kernel.org>
---
 arch/powerpc/include/asm/switch_to.h |  5 +++++
 arch/powerpc/kernel/entry_64.S       | 12 ++++++++++++
 2 files changed, 17 insertions(+)
Paul Mackerras - Aug. 7, 2013, 8:07 a.m.
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 <mikey@neuling.org>
> Cc: <stable@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.
Michael Neuling - Aug. 7, 2013, 10:55 a.m.
> > +#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); ?

Good point! 

I'd just copied the original code which was inline asm in _switch().  

Thanks,
Mikey

Patch

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
 
 /*
  * This routine switches between two different tasks.  The process