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

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Message-ID: <gsnt4ivx86sj.fsf@coltonlewis-kvm.c.googlers.com>
Date: Mon, 30 Jun 2025 17:42:52 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: 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

Oliver Upton <oliver.upton@...ux.dev> writes:

> 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.

Done.


> 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/