mttb in sys/powerpc/include/cpufunc.h still does not handle/protect-against interrupts

[Nathan Whitehorn]

We don't call mttb() in any circumstance in which interrupts are enabled 
(only in early-boot and suspend/resume contexts, and even then only on 
some hardware), so there is no need to disable them.
-Nathan

On 4/20/21 3:07 PM, Mark Millard via freebsd-ppc wrote:
> Looking at sys/powerpc/include/cpufunc.h in main (and so older too):
>
> static __inline void
> mttb(u_quad_t time)
> {
>
> 	mtspr(TBR_TBWL, 0);
> 	mtspr(TBR_TBWU, (uint32_t)(time >> 32));
> 	mtspr(TBR_TBWL, (uint32_t)(time & 0xffffffff));
> }
>
> This code still does not protect against interrupts
> (only suggestive):
>
> 	mtspr(TBR_TBWL, 0);
> HERE?
> 	mtspr(TBR_TBWU, (uint32_t)(time >> 32));
> HERE?
> 	mtspr(TBR_TBWL, (uint32_t)(time & 0xffffffff));
>
>
> My code disabled interrupts around the update:
>
> static __inline void
> mttb(u_quad_t time)
> {
> 	const uint32_t   high= time>>32;
> 	const uint32_t   low=  time&0xffffffffu;
>
> 	const register_t predisable_msr= intr_disable();
> 	mtspr(TBR_TBWL, 0);
> 	mtspr(TBR_TBWU, high);
> 	mtspr(TBR_TBWL, low);
> 	intr_restore(predisable_msr);
> }
>
> As I remember, I found powerpc documentation that indicated
> such was important to reliable settings.
>
>
> ===
> Mark Millard
> marklmi at yahoo.com
> ( dsl-only.net went
> away in early 2018-Mar)
>
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