Re: [RFC PATCH] target/arm: properly document FEAT_CRC32

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 23 Feb 2023 at 23:01, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> On 2/22/23 01:01, Alex Bennée wrote:
>> > This is a mandatory feature for Armv8.1 architectures but we don't
>> > state the feature clearly in our emulation list. While checking verify
>> > our cortex-a76 model matches up with the current TRM by breaking out
>> > the long form isar into a more modern readable FIELD_DP code.
>> >
>> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> > ---
>> >   docs/system/arm/emulation.rst |  1 +
>> >   target/arm/cpu64.c            | 29 ++++++++++++++++++++++++++---
>> >   target/arm/cpu_tcg.c          |  2 +-
>> >   3 files changed, 28 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/docs/system/arm/emulation.rst b/docs/system/arm/emulation.rst
>> > index 2062d71261..2c4fde5eef 100644
>> > --- a/docs/system/arm/emulation.rst
>> > +++ b/docs/system/arm/emulation.rst
>> > @@ -14,6 +14,7 @@ the following architecture extensions:
>> >   - FEAT_BBM at level 2 (Translation table break-before-make levels)
>> >   - FEAT_BF16 (AArch64 BFloat16 instructions)
>> >   - FEAT_BTI (Branch Target Identification)
>> > +- FEAT_CRC32 (CRC32 instruction)
>> >   - FEAT_CSV2 (Cache speculation variant 2)
>> >   - FEAT_CSV2_1p1 (Cache speculation variant 2, version 1.1)
>> >   - FEAT_CSV2_1p2 (Cache speculation variant 2, version 1.2)
>> > diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
>> > index 4066950da1..12e1a532ab 100644
>> > --- a/target/arm/cpu64.c
>> > +++ b/target/arm/cpu64.c
>> > @@ -912,6 +912,8 @@ static void aarch64_a72_initfn(Object *obj)
>> >   static void aarch64_a76_initfn(Object *obj)
>> >   {
>> >       ARMCPU *cpu = ARM_CPU(obj);
>> > +    uint64_t t;
>> > +    uint32_t u;
>> >
>> >       cpu->dtb_compatible = "arm,cortex-a76";
>> >       set_feature(&cpu->env, ARM_FEATURE_V8);
>> > @@ -928,7 +930,18 @@ static void aarch64_a76_initfn(Object *obj)
>> >       cpu->ctr = 0x8444C004;
>> >       cpu->dcz_blocksize = 4;
>> >       cpu->isar.id_aa64dfr0  = 0x0000000010305408ull;
>> > -    cpu->isar.id_aa64isar0 = 0x0000100010211120ull;
>> > +
>> > +    /* per r4p1 of the Cryptographic Extension TRM */
>> > +    t = cpu->isar.id_aa64isar0;
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, AES, 2);      /* FEAT_PMULL */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, SHA1, 1);     /* FEAT_SHA1 */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, SHA2, 1);     /* FEAT_SHA512 */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, CRC32, 1);    /* FEAT_CRC32 */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, ATOMIC, 2);   /* FEAT_LSE */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, RDM, 1);      /* FEAT_RDM */
>> > +    t = FIELD_DP64(t, ID_AA64ISAR0, DP, 1);       /* FEAT_DotProd */
>> > +    cpu->isar.id_aa64isar0 = t;
>>
>> Ok, so, this might be helpful for grepping, but it's not helpful for reading the
>> documentation, which on page B2-137 uses hex.
>
> Agreed -- we write these functions and review them by looking
> at the TRMs, and the TRMs specify the values of the ID registers
> as straight hex values.

Ahh found it now was confusing the pages with sections: B2.4 on page
B2-137. 

>
> thanks
> -- PMM


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro