linux-kernel - Re: [PATCH 1/2] KVM: arm64: Replace custom macros with fields from ID_AA64PFR0

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Date: Fri, 10 May 2024 19:09:31 +0100
From: Mark Rutland <mark.rutland@....com>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	catalin.marinas@....com, Oliver Upton <oliver.upton@...ux.dev>,
	Will Deacon <will@...nel.org>, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Fuad Tabba <tabba@...gle.com>
Subject: Re: [PATCH 1/2] KVM: arm64: Replace custom macros with fields from
 ID_AA64PFR0_EL1

On Mon, Apr 29, 2024 at 07:53:14AM +0530, Anshuman Khandual wrote:
> On 4/18/24 13:09, Marc Zyngier wrote:
> > On Thu, 18 Apr 2024 06:38:03 +0100,
> > Anshuman Khandual <anshuman.khandual@....com> wrote:
> >>  #define PVM_ID_AA64PFR0_RESTRICT_UNSIGNED (\
> >> -	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL0), ID_AA64PFR0_EL1_ELx_64BIT_ONLY) | \
> >> -	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL1), ID_AA64PFR0_EL1_ELx_64BIT_ONLY) | \
> >> -	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL2), ID_AA64PFR0_EL1_ELx_64BIT_ONLY) | \
> >> -	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL3), ID_AA64PFR0_EL1_ELx_64BIT_ONLY) | \
> >> +	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL0), ID_AA64PFR0_EL1_EL0_IMP) | \
> >> +	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL1), ID_AA64PFR0_EL1_EL1_IMP) | \
> >> +	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL2), ID_AA64PFR0_EL1_EL2_IMP) | \
> >> +	FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_EL3), ID_AA64PFR0_EL1_EL3_IMP) | \
> > 
> > If you are going to rework this, can we instead use something less
> > verbose such as SYS_FIELD_GET()?
> 
> Just wondering, is not FIELD_PREP() and SYS_FIELD_GET() does the exact opposite thing.
> The earlier builds the entire register value from various constituents, where as the
> later extracts a single register field from a complete register value instead. Or did
> I just misunderstood something here.
 
He means use one of the SYS_FIELD_*() helpers, e.g. SYS_FIELD_PREP_ENUM(), with
which this can be:

#define PVM_ID_AA64PFR0_RESTRICT_UNSIGNED (\
        SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, EL0, IMP) | \
        SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, EL1, IMP) | \
        SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, EL2, IMP) | \
        SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, EL3, IMP) | \
        SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, RAS, IMP) \
        )

.. which is far less verbose, and much easier to read.

Mark.