Re: [PATCH 2/4] mwait-idle: add SPR support

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Apr 26, 2022 at 12:05:07PM +0200, Jan Beulich wrote:
> From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> 
> Add Sapphire Rapids Xeon support.
> 
> Up until very recently, the C1 and C1E C-states were independent, but this
> has changed in some new chips, including Sapphire Rapids Xeon (SPR). In these
> chips the C1 and C1E states cannot be enabled at the same time. The "C1E
> promotion" bit in 'MSR_IA32_POWER_CTL' also has its semantics changed a bit.
> 
> Here are the C1, C1E, and "C1E promotion" bit rules on Xeons before SPR.
> 
> 1. If C1E promotion bit is disabled.
>    a. C1  requests end up with C1  C-state.
>    b. C1E requests end up with C1E C-state.
> 2. If C1E promotion bit is enabled.
>    a. C1  requests end up with C1E C-state.
>    b. C1E requests end up with C1E C-state.
> 
> Here are the C1, C1E, and "C1E promotion" bit rules on Sapphire Rapids Xeon.
> 1. If C1E promotion bit is disabled.
>    a. C1  requests end up with C1 C-state.
>    b. C1E requests end up with C1 C-state.
> 2. If C1E promotion bit is enabled.
>    a. C1  requests end up with C1E C-state.
>    b. C1E requests end up with C1E C-state.
> 
> Before SPR Xeon, the 'intel_idle' driver was disabling C1E promotion and was
> exposing C1 and C1E as independent C-states. But on SPR, C1 and C1E cannot be
> enabled at the same time.
> 
> This patch adds both C1 and C1E states. However, C1E is marked as with the
> "CPUIDLE_FLAG_UNUSABLE" flag, which means that in won't be registered by
> default. The C1E promotion bit will be cleared, which means that by default
> only C1 and C6 will be registered on SPR.
> 
> The next patch will add an option for enabling C1E and disabling C1 on SPR.
> 
> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 9edf3c0ffef0
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks, Roger.