linux-kernel - Re: [PATCH 07/10] riscv: add ISA extension parsing for Zcmop

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Message-ID: <20240411-superglue-errant-b32e5118695f@wendy>
Date: Thu, 11 Apr 2024 10:03:03 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
To: Clément Léger <cleger@...osinc.com>
CC: Deepak Gupta <debug@...osinc.com>, Conor Dooley <conor@...nel.org>,
	Jonathan Corbet <corbet@....net>, Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Rob
 Herring <robh@...nel.org>, Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>, Anup Patel <anup@...infault.org>, Shuah
 Khan <shuah@...nel.org>, Atish Patra <atishp@...shpatra.org>,
	<linux-doc@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<kvm@...r.kernel.org>, <kvm-riscv@...ts.infradead.org>,
	<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 07/10] riscv: add ISA extension parsing for Zcmop

On Thu, Apr 11, 2024 at 09:25:06AM +0200, Clément Léger wrote:
> 
> 
> On 11/04/2024 00:32, Deepak Gupta wrote:
> > On Wed, Apr 10, 2024 at 11:27:16PM +0100, Conor Dooley wrote:
> >> On Wed, Apr 10, 2024 at 11:16:11PM +0100, Conor Dooley wrote:
> >>> On Wed, Apr 10, 2024 at 02:32:41PM -0700, Deepak Gupta wrote:
> >>> > On Wed, Apr 10, 2024 at 11:11:00AM +0200, Clément Léger wrote:
> >>> > > Add parsing for Zcmop ISA extension which was ratified in commit
> >>> > > b854a709c00 ("Zcmop is ratified/1.0") of the riscv-isa-manual.
> >>> > >
> >>> > > Signed-off-by: Clément Léger <cleger@...osinc.com>
> >>> > > ---
> >>> > > arch/riscv/include/asm/hwcap.h | 1 +
> >>> > > arch/riscv/kernel/cpufeature.c | 1 +
> >>> > > 2 files changed, 2 insertions(+)
> >>> > >
> >>> > > diff --git a/arch/riscv/include/asm/hwcap.h
> >>> b/arch/riscv/include/asm/hwcap.h
> >>> > > index b7551bad341b..cff7660de268 100644
> >>> > > --- a/arch/riscv/include/asm/hwcap.h
> >>> > > +++ b/arch/riscv/include/asm/hwcap.h
> >>> > > @@ -86,6 +86,7 @@
> >>> > > #define RISCV_ISA_EXT_ZCB        77
> >>> > > #define RISCV_ISA_EXT_ZCD        78
> >>> > > #define RISCV_ISA_EXT_ZCF        79
> >>> > > +#define RISCV_ISA_EXT_ZCMOP        80
> >>> > >
> >>> > > #define RISCV_ISA_EXT_XLINUXENVCFG    127
> >>> > >
> >>> > > diff --git a/arch/riscv/kernel/cpufeature.c
> >>> b/arch/riscv/kernel/cpufeature.c
> >>> > > index 09dee071274d..f1450cd7231e 100644
> >>> > > --- a/arch/riscv/kernel/cpufeature.c
> >>> > > +++ b/arch/riscv/kernel/cpufeature.c
> >>> > > @@ -265,6 +265,7 @@ const struct riscv_isa_ext_data
> >>> riscv_isa_ext[] = {
> >>> > >     __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(zcmop, RISCV_ISA_EXT_ZCMOP),
> >>> >
> >>> > As per spec zcmop is dependent on zca. So perhaps below ?
> >>> >
> >>> > __RISCV_ISA_EXT_SUPERSET(zicboz, RISCV_ISA_EXT_ZCMOP,
> >>> RISCV_ISA_EXT_ZCA)
> >>>
> >>> What's zicboz got to do with it, copy-pasto I guess?
> > 
> > Yes, copy-pasta :-)
> > 
> >>> If we're gonna imply stuff like this though I think we need some
> >>> comments explaining why it's okay.
> >>
> >> Also, I'm inclined to call that out specifically in the binding, I've
> >> not yet checked if dependencies actually work for elements of a string
> >> array like the do for individual properties. I'll todo list that..
> > 
> > Earlier examples of specifying dependency on envcfg actually had functional
> > use case.
> > So you are right, I am not sure if its actually needed in this
> > particular case.
> 
> I actually saw that and think about addressing it but AFAICT, this
> should be handled by the machine firmware passing the isa string to the
> kernel (ie, it should be valid). In the case of QEMU, it takes care of
> setting the extension that are required by this extension itself.
> 
> If we consider to have potentially broken isa string (ie extensions
> dependencies not correctly handled), then we'll need some way to
> validate this within the kernel.

No, the DT passed to the kernel should be correct and we by and large we
should not have to do validation of it. What I meant above was writing
the binding so that something invalid will not pass dtbs_check.

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