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

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Date:   Tue, 5 May 2020 13:12:39 +0100
From:   Will Deacon <will@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
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 12:50:54PM +0100, Mark Rutland wrote:
> 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:
> > > > > 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).

Ok, I added a comment below.

Will

--->8

commit be7ab6a6cdb0a6d7b10883094c2adf96f5d4e1e8
Author: Will Deacon <will@...nel.org>
Date:   Tue May 5 13:08:02 2020 +0100

    arm64: cpufeature: Group indexed system register definitions by name
    
    Some system registers contain an index in the name (e.g. ID_MMFR<n>_EL1)
    and, while this index often follows the register encoding, newer additions
    to the architecture are necessarily tacked on the end. Sorting these
    registers by encoding therefore becomes a bit of a mess.
    
    Group the indexed system register definitions by name so that it's easier to
    read and will hopefully reduce the chance of us accidentally introducing
    duplicate definitions in the future.
    
    Signed-off-by: Will Deacon <will@...nel.org>

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 2dd3f4ca9780..194684301df0 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -105,6 +105,10 @@
 #define SYS_DC_CSW			sys_insn(1, 0, 7, 10, 2)
 #define SYS_DC_CISW			sys_insn(1, 0, 7, 14, 2)
 
+/*
+ * System registers, organised loosely by encoding but grouped together
+ * where the architected name contains an index. e.g. ID_MMFR<n>_EL1.
+ */
 #define SYS_OSDTRRX_EL1			sys_reg(2, 0, 0, 0, 2)
 #define SYS_MDCCINT_EL1			sys_reg(2, 0, 0, 2, 0)
 #define SYS_MDSCR_EL1			sys_reg(2, 0, 0, 2, 2)
@@ -140,6 +144,7 @@
 #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 +152,6 @@
 #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)