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From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 17 Mar 2014 13:03:14 +0000
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Subject: Re: [Qemu-devel] [PATCH v4 13/21] target-arm: Use dedicated CPU
 state fields for ARM946 access bit registers
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To: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: Rob Herring <rob.herring@linaro.org>, Patch Tracking <patches@linaro.org>, Michael Matz <matz@suse.de>, Claudio Fontana <claudio.fontana@huawei.com>, Alexander Graf <agraf@suse.de>, "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, Laurent Desnogues <laurent.desnogues@gmail.com>, Dirk Mueller <dmueller@suse.de>, Will Newton <will.newton@linaro.org>, =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>, Christoffer Dall <christoffer.dall@linaro.org>, Richard Henderson <rth@twiddle.net>

On 17 March 2014 05:20, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
> On Fri, Mar 7, 2014 at 5:32 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
>>  static const ARMCPRegInfo pmsav5_cp_reginfo[] = {
>>      { .name = "DATA_AP", .cp = 15, .crn = 5, .crm = 0, .opc1 = 0, .opc2 = 0,
>>        .access = PL1_RW, .type = ARM_CP_NO_MIGRATE,
>> -      .fieldoffset = offsetof(CPUARMState, cp15.c5_data), .resetvalue = 0,
>> +      .fieldoffset = offsetof(CPUARMState, cp15.pmsav5_data_ap),
>> +      .resetvalue = 0,
>
> I know its just motion of existing code, but what's the policy on zero
> resets? Can we leave them out for brevity? Checkpatch complains when a
> global is explictly 0 initialized, so it seems sane that the same rule
> applies to individual fields (just checkpatch probably has hard time
> figuring this one out).

The semantics allow you to leave out .resetvalue if it is 0; I think
generally when I've written reginfo definitions I've tended to put
in the .resetvalue as an indication of "I know this reginfo needs
a reset value and it is zero" as opposed to "I didn't think about
reset when I wrote this".

We definitely don't want checkpatch to warn about explicit zero
initializers in structs like this, otherwise we wouldn't be
able to say ".crm = 0, .opc1 = 0, .opc2 = 0", which would be
less comprehensible than writing them out explicitly I think.

thanks
-- PMM