* Yazen Ghannam <yazen.ghan...@amd.com> wrote:
> From: Yazen Ghannam <yazen.ghan...@amd.com>
>
> Recent AMD systems support using MWAIT for C1 state. However, MWAIT will
> not allow deeper cstates than C1 on current systems.
>
> With play_dead() we expect the OS to use the deepest state available.
> The deepest state available on AMD systems is reached through SystemIO
> or HALT. If MWAIT is available, we use it instead of the other methods,
> so we never reach the deepest state.
>
> Don't try to use MWAIT to play_dead() on AMD systems. Instead, we'll use
> CPUIDLE to enter the deepest state advertised by firmware. If CPUIDLE is
> not available then we fallback to HALT.
>
> Signed-off-by: Yazen Ghannam <yazen.ghan...@amd.com>
> ---
> arch/x86/kernel/smpboot.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index ff99e2b6fc54..67cf00b25f83 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1536,6 +1536,9 @@ static inline void mwait_play_dead(void)
> void *mwait_ptr;
> int i;
>
> + /* Don't try native MWAIT on AMD. Stick to CPUIDLE and HALT. */
> + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
> + return;
The comment should mainly explain the 'why is this done', not the 'what is
done'
which is pretty obvious from the code ...
Thanks,
Ingo
