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Date:   Thu, 01 Apr 2021 18:01:29 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v2] powerpc/traps: Enhance readability for trap types
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Segher Boessenkool <segher@kernel.crashing.org>
Cc:     aik@ozlabs.ru, akpm@linux-foundation.org, alistair@popple.id.au,
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        benh@kernel.crashing.org, christophe.leroy@csgroup.eu,
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        peterz@infradead.org, pmladek@suse.com,
        ravi.bangoria@linux.ibm.com, rppt@kernel.org,
        Xiongwei Song <sxwjean@gmail.com>,
        Xiongwei Song <sxwjean@me.com>
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        <875z17y79i.fsf@mpe.ellerman.id.au>
        <20210331212550.GD13863@gate.crashing.org>
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Excerpts from Michael Ellerman's message of April 1, 2021 12:39 pm:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
>> On Wed, Mar 31, 2021 at 08:58:17PM +1100, Michael Ellerman wrote:
>>> So perhaps:
>>>=20
>>>   EXC_SYSTEM_RESET
>>>   EXC_MACHINE_CHECK
>>>   EXC_DATA_STORAGE
>>>   EXC_DATA_SEGMENT
>>>   EXC_INST_STORAGE
>>>   EXC_INST_SEGMENT
>>>   EXC_EXTERNAL_INTERRUPT
>>>   EXC_ALIGNMENT
>>>   EXC_PROGRAM_CHECK
>>>   EXC_FP_UNAVAILABLE
>>>   EXC_DECREMENTER
>>>   EXC_HV_DECREMENTER
>>>   EXC_SYSTEM_CALL
>>>   EXC_HV_DATA_STORAGE
>>>   EXC_PERF_MONITOR
>>
>> These are interrupt (vectors), not exceptions.  It doesn't matter all
>> that much, but confusing things more isn't useful either!  There can be
>> multiple exceptions that all can trigger the same interrupt.
>=20
> Yeah I know, but I think that ship has already sailed as far as the
> naming we have in the kernel.

It has, but there are also several other ships also sailing in different=20
directions. It could be worse though, at least they are not sideways in=20
the Suez.

> We have over 250 uses of "exc", and several files called "exception"
> something.
>=20
> Using "interrupt" can also be confusing because Linux uses that to mean
> "external interrupt".
>=20
> But I dunno, maybe INT or VEC is clearer? .. or TRAP :)

We actually already have defines that follow Segher's suggestion, it's=20
just that they're hidden away in a KVM header.

#define BOOK3S_INTERRUPT_SYSTEM_RESET   0x100
#define BOOK3S_INTERRUPT_MACHINE_CHECK  0x200
#define BOOK3S_INTERRUPT_DATA_STORAGE   0x300
#define BOOK3S_INTERRUPT_DATA_SEGMENT   0x380
#define BOOK3S_INTERRUPT_INST_STORAGE   0x400
#define BOOK3S_INTERRUPT_INST_SEGMENT   0x480
#define BOOK3S_INTERRUPT_EXTERNAL       0x500
#define BOOK3S_INTERRUPT_EXTERNAL_HV    0x502
#define BOOK3S_INTERRUPT_ALIGNMENT      0x600

It would take just a small amount of work to move these to general=20
powerpc header, add #ifdefs for Book E/S where the numbers differ,
and remove the BOOK3S_ prefix.

I don't mind INTERRUPT_ but INT_ would be okay too. VEC_ actually
doesn't match what Book E does (which is some weirdness to map some
of them to match Book S but not all, arguably we should clean that
up too and just use vector numbers consistently, but the INTERRUPT_
prefix would still be valid if we did that).

BookE KVM entry will still continue to use a different convention
there so I would leave all those KVM defines in place for now, we
might do another pass on them later.

Thanks,
Nick