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Re: [PATCH v2 09/10] target/arm: Allow M-profile CPUs with FP16 to set F
From: |
Richard Henderson |
Subject: |
Re: [PATCH v2 09/10] target/arm: Allow M-profile CPUs with FP16 to set FPSCR.FP16 |
Date: |
Mon, 19 Oct 2020 08:57:21 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 10/19/20 8:13 AM, Peter Maydell wrote:
> M-profile CPUs with half-precision floating point support should
> be able to write to FPSCR.FZ16, but an M-profile specific masking
> of the value at the top of vfp_set_fpscr() currently prevents that.
> This is not yet an active bug because we have no M-profile
> FP16 CPUs, but needs to be fixed before we can add any.
>
> The bits that the masking is effectively preventing from being
> set are the A-profile only short-vector Len and Stride fields,
> plus the Neon QC bit. Rearrange the order of the function so
> that those fields are handled earlier and only under a suitable
> guard; this allows us to drop the M-profile specific masking,
> making FZ16 writeable.
>
> This change also makes the QC bit correctly RAZ/WI for older
> no-Neon A-profile cores.
>
> This refactoring also paves the way for the low-overhead-branch
> LTPSIZE field, which uses some of the bits that are used for
> A-profile Stride and Len.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> target/arm/vfp_helper.c | 47 ++++++++++++++++++++++++-----------------
> 1 file changed, 28 insertions(+), 19 deletions(-)
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
- [PATCH v2 02/10] target/arm: Implement v8.1M NOCP handling, (continued)
- [PATCH v2 02/10] target/arm: Implement v8.1M NOCP handling, Peter Maydell, 2020/10/19
- [PATCH v2 07/10] target/arm: Implement v8.1M low-overhead-loop instructions, Peter Maydell, 2020/10/19
- [PATCH v2 10/10] target/arm: Implement FPSCR.LTPSIZE for M-profile LOB extension, Peter Maydell, 2020/10/19
- [PATCH v2 04/10] target/arm: Make the t32 insn[25:23]=111 group non-overlapping, Peter Maydell, 2020/10/19
- [PATCH v2 06/10] target/arm: Implement v8.1M branch-future insns (as NOPs), Peter Maydell, 2020/10/19
- [PATCH v2 05/10] target/arm: Don't allow BLX imm for M-profile, Peter Maydell, 2020/10/19
- [PATCH v2 09/10] target/arm: Allow M-profile CPUs with FP16 to set FPSCR.FP16, Peter Maydell, 2020/10/19
- Re: [PATCH v2 09/10] target/arm: Allow M-profile CPUs with FP16 to set FPSCR.FP16,
Richard Henderson <=
- [PATCH v2 08/10] target/arm: Fix has_vfp/has_neon ID reg squashing for M-profile, Peter Maydell, 2020/10/19