Re: [RFC PATCH] powerpc: enable cpu clock for powerpc64

[Jens Axboe <axboe@kernel.dk>]

On 12/03/2015 10:50 PM, Li Zhong wrote:
> This patch tries to enable cpu clock for powerpc64, the code is copied from
> mftb() in kernel source.
>
> The two instructions after mfspr are added in the kernel to solve an erratum on
> Cell and fsl booke CPUs. On those CPUs, 64 bits mftb is not atomic, so it is
> possible that the low order 32 bits are already reset to 0x00000000 but the
> high order bits are not yet incremented by one.
>
> Don't know how to tell whether it will be running on those CPUs or not, I just
> keep the above fix for all ppc64 CPUs. Even if we have some method to check
> whether we are on those CPUs or not at run time, I think the check won't cost
> less than the two added instructions. Maybe we could use the similar fix up
> code kernel uses to dynamically patch the instructions with nops if not needed.
> But that would add much more complexity.

Thanks, applied. I don't have any powerpc hw, so I'll depend on your 
testing for this.

-- 
Jens Axboe