linux-kernel - Re: [PATCH V3 04/16] arm64/cpufeature: Introduce ID

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Date:   Tue, 5 May 2020 12:50:54 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 04/16] arm64/cpufeature: Introduce ID_PFR2 CPU register

On Tue, May 05, 2020 at 12:27:19PM +0100, Will Deacon wrote:
> On Tue, May 05, 2020 at 12:16:07PM +0100, Mark Rutland wrote:
> > On Tue, May 05, 2020 at 12:12:41PM +0100, Will Deacon wrote:
> > > On Sat, May 02, 2020 at 07:03:53PM +0530, Anshuman Khandual wrote:
> > > > This adds basic building blocks required for ID_PFR2 CPU register which
> > > > provides information about the AArch32 programmers model which must be
> > > > interpreted along with ID_PFR0 and ID_PFR1 CPU registers. This is added
> > > > per ARM DDI 0487F.a specification.
> > > > 
> > > > Cc: Catalin Marinas <catalin.marinas@....com>
> > > > Cc: Will Deacon <will@...nel.org>
> > > > Cc: Marc Zyngier <maz@...nel.org>
> > > > Cc: Mark Rutland <mark.rutland@....com>
> > > > Cc: James Morse <james.morse@....com>
> > > > Cc: Suzuki K Poulose <suzuki.poulose@....com>
> > > > Cc: kvmarm@...ts.cs.columbia.edu
> > > > Cc: linux-arm-kernel@...ts.infradead.org
> > > > Cc: linux-kernel@...r.kernel.org
> > > > 
> > > > Suggested-by: Mark Rutland <mark.rutland@....com>
> > > > Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> > > > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > > > ---
> > > >  arch/arm64/include/asm/cpu.h    |  1 +
> > > >  arch/arm64/include/asm/sysreg.h |  4 ++++
> > > >  arch/arm64/kernel/cpufeature.c  | 11 +++++++++++
> > > >  arch/arm64/kernel/cpuinfo.c     |  1 +
> > > >  arch/arm64/kvm/sys_regs.c       |  2 +-
> > > >  5 files changed, 18 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h
> > > > index b4a40535a3d8..464e828a994d 100644
> > > > --- a/arch/arm64/include/asm/cpu.h
> > > > +++ b/arch/arm64/include/asm/cpu.h
> > > > @@ -46,6 +46,7 @@ struct cpuinfo_arm64 {
> > > >  	u32		reg_id_mmfr3;
> > > >  	u32		reg_id_pfr0;
> > > >  	u32		reg_id_pfr1;
> > > > +	u32		reg_id_pfr2;
> > > >  
> > > >  	u32		reg_mvfr0;
> > > >  	u32		reg_mvfr1;
> > > > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > > > index e5317a6367b6..c977449e02db 100644
> > > > --- a/arch/arm64/include/asm/sysreg.h
> > > > +++ b/arch/arm64/include/asm/sysreg.h
> > > > @@ -153,6 +153,7 @@
> > > >  #define SYS_MVFR0_EL1			sys_reg(3, 0, 0, 3, 0)
> > > >  #define SYS_MVFR1_EL1			sys_reg(3, 0, 0, 3, 1)
> > > >  #define SYS_MVFR2_EL1			sys_reg(3, 0, 0, 3, 2)
> > > > +#define SYS_ID_PFR2_EL1			sys_reg(3, 0, 0, 3, 4)
> > > 
> > > nit: but please group these defines by name rather than encoding.
> > 
> > So far we've *always* grouped these by encoding in this file, so can we
> > keep things that way for now? Otherwise we're inconsistent with both
> > schemes.
> 
> Hmm, but it's really hard to read sorted that way and we'll end up with
> duplicate definitions like we had for some of the field offsets already.

I appreciate that, and don't disagree that the current scheme is not
obvious.

I just want to ensure that we don't make things less consistent, and if
we're going to change the scheme in order to make that easier, it should
be a separate patch. There'll be other changes like MMFR4_EL1, and we
should probably add a comment as to what the policy is either way (e.g.
if we're just grouping at the top level, or if that should be sorted
too).

Thanks,
Mark.

> The only ID register that seems to be out of place atm is MMFR4, which I
> can move (see below)
> 
> Will
> 
> --->8
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 2dd3f4ca9780..137201ea383b 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -140,6 +140,7 @@
>  #define SYS_ID_MMFR1_EL1		sys_reg(3, 0, 0, 1, 5)
>  #define SYS_ID_MMFR2_EL1		sys_reg(3, 0, 0, 1, 6)
>  #define SYS_ID_MMFR3_EL1		sys_reg(3, 0, 0, 1, 7)
> +#define SYS_ID_MMFR4_EL1		sys_reg(3, 0, 0, 2, 6)
>  
>  #define SYS_ID_ISAR0_EL1		sys_reg(3, 0, 0, 2, 0)
>  #define SYS_ID_ISAR1_EL1		sys_reg(3, 0, 0, 2, 1)
> @@ -147,7 +148,6 @@
>  #define SYS_ID_ISAR3_EL1		sys_reg(3, 0, 0, 2, 3)
>  #define SYS_ID_ISAR4_EL1		sys_reg(3, 0, 0, 2, 4)
>  #define SYS_ID_ISAR5_EL1		sys_reg(3, 0, 0, 2, 5)
> -#define SYS_ID_MMFR4_EL1		sys_reg(3, 0, 0, 2, 6)
>  #define SYS_ID_ISAR6_EL1		sys_reg(3, 0, 0, 2, 7)
>  
>  #define SYS_MVFR0_EL1			sys_reg(3, 0, 0, 3, 0)