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Re: [PATCH for-4.22 v2 2/8] x86/mwait-idle: clean up BYT/CHT auto demotion disable
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 14 May 2026 16:10:24 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Thu, 14 May 2026 14:10:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, May 12, 2026 at 05:36:06PM +0200, Jan Beulich wrote:
> Bay Trail (BYT) and Cherry Trail (CHT) platforms have a very specific way
> of disabling auto-demotion via specific MSR bits. Clean up the code so that
> BYT/CHT-specifics do not show up in the common 'struct idle_cpu' data
> structure.
>
> Remove the 'byt_auto_demotion_disable_flag' flag from 'struct idle_cpu',
> because a better coding pattern is to avoid very case-specific fields like
> 'bool byt_auto_demotion_disable_flag' in a common data structure, which is
> used for all platforms, not only BYT/CHT. The code is just more readable
> when common data structures contain only commonly used fields.
>
> Instead, match BYT/CHT in the 'intel_idle_init_cstates_icpu()' function,
> and introduce a small helper to take care of BYT/CHT auto-demotion. This
> is consistent with how platform-specific things are done for other
> platforms.
>
> No intended functional changes.
>
> Inspired by (and description largely taken from) Linux'es c93d13b661a6
> ("intel_idle: clean up BYT/CHT auto demotion disable").
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks, Roger.
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