From: Philipp Tomsich <philipp.tomsich@vrull.eu>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: qemu-devel@nongnu.org,
Alistair Francis <alistair.francis@wdc.com>,
Bin Meng <bin.meng@windriver.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
qemu-riscv@nongnu.org
Subject: Re: [PATCH 1/2] target/riscv: fence.i: update decode pattern
Date: Fri, 12 Aug 2022 16:09:19 +0200 [thread overview]
Message-ID: <CAAeLtUDbVwvQzr9u+D2KH6qBoiu4ikEbf3aVahbmK_i=6gEM7A@mail.gmail.com> (raw)
In-Reply-To: <20220812140103.3lbh45oidiw2fhsf@kamzik>
On Fri, 12 Aug 2022 at 16:01, Andrew Jones <ajones@ventanamicro.com> wrote:
>
> > Update the decode pattern to reflect the specification.
>
> I got hung-up on this for a bit since there isn't any "must-be-0" fields,
Please refer to '“Zifencei” Instruction-Fetch Fence, Version 2.0' in
the specification.
The encoding diagram clearly states 0 for imm[11:0], 0 for rs1 and 0 for rd.
However, there is an explanatory paragraph below (unfortunately, it is
not clear whether this is normative or informative):
> The unused fields in the FENCE.I instruction, imm[11:0], rs1, and rd, are reserved for finer-grain fences in future extensions. For forward compatibility, base implementations shall ignore these fields, and standard software shall zero these fields.
Strictly speaking, this patch may be too restrictive (it violates the
"for forward-compatibility" part — which I consider informative only,
though).
Thanks,
Philipp.
next prev parent reply other threads:[~2022-08-12 14:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-12 13:13 [PATCH 1/2] target/riscv: fence.i: update decode pattern Philipp Tomsich
2022-08-12 13:13 ` [PATCH 2/2] target/riscv: fence: reconcile with specification Philipp Tomsich
2022-08-12 13:21 ` Peter Maydell
2022-08-12 14:17 ` Philipp Tomsich
2022-09-08 9:24 ` Alistair Francis
2022-09-08 9:28 ` Philipp Tomsich
2022-08-12 14:03 ` Andrew Jones
2022-08-12 14:01 ` [PATCH 1/2] target/riscv: fence.i: update decode pattern Andrew Jones
2022-08-12 14:09 ` Philipp Tomsich [this message]
2022-08-12 14:18 ` Peter Maydell
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