linux-kernel - Re: [PATCH v3 02/22] arm64: Generate sign macro for sysreg Enums

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Message-ID: <aF8FPTupC_VnAldN@linux.dev>
Date: Fri, 27 Jun 2025 13:55:25 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Colton Lewis <coltonlewis@...gle.com>
Cc: Ben Horgan <ben.horgan@....com>, kvm@...r.kernel.org,
	pbonzini@...hat.com, corbet@....net, linux@...linux.org.uk,
	catalin.marinas@....com, will@...nel.org, maz@...nel.org,
	mizhang@...gle.com, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, mark.rutland@....com, shuah@...nel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 02/22] arm64: Generate sign macro for sysreg Enums

On Fri, Jun 27, 2025 at 08:45:38PM +0000, Colton Lewis wrote:
> Hi Ben. Thanks for the review.
> 
> Ben Horgan <ben.horgan@....com> writes:
> 
> > Hi Colton,
> 
> > On 6/26/25 21:04, Colton Lewis wrote:
> > > There's no reason Enums shouldn't be equivalent to UnsignedEnums and
> > > explicitly specify they are unsigned. This will avoid the annoyance I
> > > had with HPMN0.
> > An Enum can be annotated with the field's sign by updating it to
> > UnsignedEnum or SignedEnum. This is explained in [1].
> 
> > With this change ID_AA64PFR1_EL1.MTE_frac would be marked as unsigned
> > when it should really be considered signed.
> 
> > Enum	43:40	MTE_frac
> > 	0b0000	ASYNC
> > 	0b1111	NI
> > EndEnum
> 
> Thanks for the explanation. I made this a separate commit because I
> considered people might object and HPMN0 is already an UnsignedEnum in
> my previous commit.
> 
> Do you think it would be a good idea to make plain Enums signed by
> default or should I just remove this commit from the series?

It is presumptive to associate a sign with an enumeration. Generally
speaking, the only fields that can do signed / unsigned comparisons are
the Feature ID register fields.

So please drop this and only keep the change for HPMN0.

Thanks,
Oliver

> > > Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
> > > ---
> > >    arch/arm64/tools/gen-sysreg.awk | 1 +
> > >    1 file changed, 1 insertion(+)
> 
> > > diff --git a/arch/arm64/tools/gen-sysreg.awk
> > > b/arch/arm64/tools/gen-sysreg.awk
> > > index f2a1732cb1f6..fa21a632d9b7 100755
> > > --- a/arch/arm64/tools/gen-sysreg.awk
> > > +++ b/arch/arm64/tools/gen-sysreg.awk
> > > @@ -308,6 +308,7 @@ $1 == "Enum" && (block_current() == "Sysreg" ||
> > > block_current() == "SysregFields
> > >    	parse_bitdef(reg, field, $2)
> 
> > >    	define_field(reg, field, msb, lsb)
> > > +	define_field_sign(reg, field, "false")
> 
> > >    	next
> > >    }
> 
> > Thanks,
> 
> > Ben
> 
> > [1]
> > https://lore.kernel.org/all/20221207-arm64-sysreg-helpers-v4-1-25b6b3fb9d18@kernel.org/