Re: [PATCH v3 2/3] RISC-V: uapi: add HWCAP for Bitmanip/Scalar Crypto

Conor Dooley
2022-11-24T17:54:09Z

On 24/11/2022 17:34, Samuel Ortiz wrote:
> On Thu, Nov 24, 2022 at 05:20:37PM +0000, Conor Dooley wrote:
>> On 24/11/2022 17:12, Samuel Ortiz wrote:
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>>>
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>>> On Thu, Nov 24, 2022 at 11:55:01AM +0000, Conor Dooley wrote:
>>>> On Thu, Nov 24, 2022 at 11:47:30AM +0100, Samuel Ortiz wrote:
>>>>
>>>>> Patch #1 is definitely needed regardless of which interface we pick for
>>>>> exposing the ISA strings to userspace.
>>>>
>>>> I took another look at #1, and I feel more confused about what
>>>> constitutes canonical order than I did before! If you know better than
>>>> I, and you probably do since you're interested in these 6 month old
>>>> patches, some insight would be appreciated!
>>>
>>> Assuming we don't go with hwcap, I dont think the order of the
>>> riscv_isa_ext_id enum matters that much?
>>
>> The chief put it in canonical order so that's good enough for me!
>>
>>>
>>> iiuc we're building the cpuinfo string from the riscv_isa_ext_data
>>> array, and I think the current code is incorrect:
>>>
>>> static struct riscv_isa_ext_data isa_ext_arr[] = {
>>> __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>>> __RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
>>> __RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>>> __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
>>> __RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
>>> __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
>>> __RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
>>> };
>>>
>>> zicbom and zihintpause should come before supervisor level extensions.
>>> I'm going to send a patch for that.
>>
>> idk, Palmer explicitly re-ordered this:
>> https://lore.kernel.org/linux-riscv/20220920204518.10988-1-palmer@rivosinc.com/
>>
>> By my reading of the isa manual, what Palmer did is correct as
>> those are not "Additional Standard Extensions". /shrug
>
> Hmm, by their name (Z[a-b]+) they are Additional Standard Extensions.
> What am I missing?

Right, and this is where I get confused. Zam and Ztso *are* Additional
Standard Extensions, I think we can agree on that one? For those
extensions:
\chapter{``Ztso'' Standard Extension for Total Store Ordering, v0.1}
\chapter{``Zam'' Standard Extension for Misaligned Atomics, v0.1}

They're also called out specifically in the table:
https://github.com/riscv/riscv-isa-manual/blob/master/src/naming.tex#L147

For Zihintpause however:
\chapter{``Zihintpause'' Pause Hint, Version 2.0}

See what I mean? I looked at the specs for the bitmanip stuff and for
crypto, which both never mention being standard.

That table has the caption:
> The table also defines the canonical order in which extension names
> must appear in the name string, with top-to-bottom in table
> indicating first-to-last in the name string.

It only calls out Zicsr, Zifencei, Zam and Ztso are being permitted
before Sdef, but as I said I am not a specs person, so perhaps some
of the extensions in question are intended to go there but have not
yet been merged into the isa manual doc. Zihintpause *is* in the
isa manual though but not specifically called out.

Anyways, hopefully that at least helps with my line of thinking!

Conor.