[OpenWrt-Devel] [RFC] Mips SIMD architecture (MSA)

[José Vázquez]

2015-04-13 11:15 GMT+02:00, Paul Burton <paul.burton at imgtec.com>:
> On Mon, Apr 13, 2015 at 10:54:05AM +0200, José Vázquez wrote:
>> As far i can understand MSA is a feature that is only present in the
>> MIPS Warrior cores and, for now, seems that could be only needed in
>> malta [1] target.
>> As you can see in arch/mips/Kconfig MIPS32R2 and MIPS64R2 select
>> CPU_SUPPORTS_MSA which does not apply to the majority of the mips
>> targets in OpenWRT.
>> Deleting "select CPU_SUPPORTS_MSA" in [2] and [3] and changing [4]
>> with "depends CPU_MIPS32_R2 || CPU_MIPS64_R2" will make MSA selectable
>> and should make the kernel smaller.
>
> Hello,
>
> I'm not sure I understand the problem here - CPU_HAS_MSA should already
> be configurable via Kconfig, so you can just disable it if you don't
> need it (as indicated in the Kconfig help text). The CPU_SUPPORTS_MSA
> entries are there just to enforce that you can only enable CPU_HAS_MSA
> on a system which might possibly include MSA (ie. MIPSr2+, well really
> MIPSr5+).
>
> In essence, the fact that your system selects CPU_SUPPORTS_MSA shouldn't
> increase the size of your kernel unless you also enable the configurable
> CPU_HAS_MSA. Am I missing something?
>
> Thanks,
>     Paul
>
>> [1]https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/arch/mips/Kconfig?id=refs/tags/v3.18.11#n311
>> [2]https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/arch/mips/Kconfig?id=refs/tags/v3.18.11#n1256
>> [3]https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/arch/mips/Kconfig?id=refs/tags/v3.18.11#n1290
>> [4]https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/arch/mips/Kconfig?id=refs/tags/v3.18.11#n2135
>>
>> Regards:
>>
>> Pepe
>>
MSA is not selectable if in Kconfig the target selects
SYS_HAS_CPU_MIPS32_R2 or SYS_HAS_CPU_MIPS64_R2, like Lantiq, PMC_MSP,
Ralink and some others because of [2] and [3].
I.e., in the case of EVA it is only selected if SYS_HAS_CPU_MIPS32_R3_5.

Pepe
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