Re: [PATCH v2 04/12] riscv: add ISA parsing for Zca, Zcf, Zcd and Zcb

From: Conor Dooley <conor.dooley@microchip.com>
To: "Clément Léger" <cleger@rivosinc.com>
Cc: Conor Dooley <conor@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Anup Patel <anup@brainfault.org>, Shuah Khan <shuah@kernel.org>,
	Atish Patra <atishp@atishpatra.org>, <linux-doc@vger.kernel.org>,
	<linux-riscv@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <kvm@vger.kernel.org>,
	<kvm-riscv@lists.infradead.org>,
	<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH v2 04/12] riscv: add ISA parsing for Zca, Zcf, Zcd and Zcb
Date: Mon, 22 Apr 2024 10:35:21 +0100	[thread overview]
Message-ID: <20240422-daylight-sassy-ff3b0d867fef@wendy> (raw)
In-Reply-To: <6ab9e591-f2f2-4267-8bdd-169ef0243e14@rivosinc.com>

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On Mon, Apr 22, 2024 at 10:53:10AM +0200, Clément Léger wrote:
> On 19/04/2024 17:51, Conor Dooley wrote:
> > On Thu, Apr 18, 2024 at 02:42:27PM +0200, Clément Léger wrote:
> >> The Zc* standard extension for code reduction introduces new extensions.
> >> This patch adds support for Zca, Zcf, Zcd and Zcb. Zce, Zcmt and Zcmp
> >> are left out of this patch since they are targeting microcontrollers/
> >> embedded CPUs instead of application processors.
> >>
> >> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> >> ---
> >>  arch/riscv/include/asm/hwcap.h | 4 ++++
> >>  arch/riscv/kernel/cpufeature.c | 4 ++++
> >>  2 files changed, 8 insertions(+)
> >>
> >> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> >> index 543e3ea2da0e..b7551bad341b 100644
> >> --- a/arch/riscv/include/asm/hwcap.h
> >> +++ b/arch/riscv/include/asm/hwcap.h
> >> @@ -82,6 +82,10 @@
> >>  #define RISCV_ISA_EXT_ZACAS		73
> >>  #define RISCV_ISA_EXT_XANDESPMU		74
> >>  #define RISCV_ISA_EXT_ZIMOP		75
> >> +#define RISCV_ISA_EXT_ZCA		76
> >> +#define RISCV_ISA_EXT_ZCB		77
> >> +#define RISCV_ISA_EXT_ZCD		78
> >> +#define RISCV_ISA_EXT_ZCF		79
> >>  
> >>  #define RISCV_ISA_EXT_XLINUXENVCFG	127
> >>  
> >> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> >> index 115ba001f1bc..09dee071274d 100644
> >> --- a/arch/riscv/kernel/cpufeature.c
> >> +++ b/arch/riscv/kernel/cpufeature.c
> >> @@ -261,6 +261,10 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> >>  	__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
> >>  	__RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
> >>  	__RISCV_ISA_EXT_DATA(zfhmin, RISCV_ISA_EXT_ZFHMIN),
> >> +	__RISCV_ISA_EXT_DATA(zca, RISCV_ISA_EXT_ZCA),
> >> +	__RISCV_ISA_EXT_DATA(zcb, RISCV_ISA_EXT_ZCB),
> >> +	__RISCV_ISA_EXT_DATA(zcd, RISCV_ISA_EXT_ZCD),
> >> +	__RISCV_ISA_EXT_DATA(zcf, RISCV_ISA_EXT_ZCF),
> >>  	__RISCV_ISA_EXT_DATA(zba, RISCV_ISA_EXT_ZBA),
> >>  	__RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
> >>  	__RISCV_ISA_EXT_DATA(zbc, RISCV_ISA_EXT_ZBC),
> > 
> > Ye, this looks exactly like what I "feared".
> 
> Ok but for instance, Qemu actually set Zc* based on C/F/D. So the ISA
> string containing theses dependencies should actually also be allowed.
> So should we simply ignore them in the ISA string and always do our own
> "post-processing" based on C/F/D?

I'm not familiar with the contents of all of these extensions, but I
assume the reasoning for splitting them out is that you can implement
them but not maybe not implement C (or something similar)? If that's the
case, you cannot always imply.

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