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

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Date: Thu, 11 Apr 2024 09:25:06 +0200
From: Clément Léger <cleger@...osinc.com>
To: Deepak Gupta <debug@...osinc.com>, Conor Dooley <conor@...nel.org>
Cc: 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 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.

Clément

> 
> And yes definitley, dependency should be mentioned in binding.
> 
>