On Wed, Feb 28, 2024 at 8:28 AM He Rongguang
<herongguang@xxxxxxxxxxxxxxxxx> wrote:
>
> According to x86 manual (Intel SDM Vol 2, Table 4-11. MWAIT Hints
> Register (EAX) and AMD manual Vol 3, MWAIT), mwait hint[7:4] adds 1 is
> the corresponding cstate, and 0xF means C0, so fix the handling of
> 0xF -> C0.
>
> Intel: "Value of 0 means C1; 1 means C2 and so on
> Value of 01111B means C0".
>
> AMD: "The processor C-state is EAX[7:4]+1, so to request C0 is to place
> the value F in EAX[7:4] and to request C1 is to place the value 0 in
> EAX[7:4].".
Yes, 0x0F is defined to correspond to C0. However, the value in
question is never equal to 0x0F in any of the functions modified by
this patch.
What's the purpose of the modification, then?
> Signed-off-by: He Rongguang <herongguang@xxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kernel/acpi/cstate.c | 4 ++--
> drivers/idle/intel_idle.c | 3 ++-
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index 401808b47af3..f3ffd0a3a012 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -131,8 +131,8 @@ static long acpi_processor_ffh_cstate_probe_cpu(void
> *_cx)
> cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
>
> /* Check whether this particular cx_type (in CST) is supported
> or not */
> - cstate_type = ((cx->address >> MWAIT_SUBSTATE_SIZE) &
> - MWAIT_CSTATE_MASK) + 1;
> + cstate_type = (((cx->address >> MWAIT_SUBSTATE_SIZE) &
> + MWAIT_CSTATE_MASK) + 1) & MWAIT_CSTATE_MASK;
> edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
> num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
>
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index bcf1198e8991..e486027f8b07 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1934,7 +1934,8 @@ static void __init spr_idle_state_table_update(void)
>
> static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
> {
> - unsigned int mwait_cstate = MWAIT_HINT2CSTATE(mwait_hint) + 1;
> + unsigned int mwait_cstate = (MWAIT_HINT2CSTATE(mwait_hint) + 1) &
> + MWAIT_CSTATE_MASK;
> unsigned int num_substates = (mwait_substates >> mwait_cstate *
> 4) &
> MWAIT_SUBSTATE_MASK;
>
> --
