[PATCH] drm/amd/display: Limit DCN to x86 arch

[Dave Airlie]

On 20 May 2017 at 05:36, Harry Wentland <harry.wentland at amd.com> wrote:
> On 2017-05-19 11:02 AM, Christian König wrote:
>>
>> Am 19.05.2017 um 16:01 schrieb Harry Wentland:
>>>
>>> DCN bw calcs currently rely on the following gcc options:
>>>    -mhard-float -msse -mpreferred-stack-boundary=4
>>
>>
>> Mhm, price question: Why does DCN rely on the gcc options?
>>
>
> Tony and Dmytro can probably provide more info here but my understanding is
> that DCN bandwidth calcs requires floating point support. This code comes
> pretty much straight from hardware teams with a guarantee that the output is
> good.
>
> If we were to rewrite bandwidth calculations that guarantee would basically
> fly out the window, which means when there's a bandwidth bug we cannot
> easily get HW support unless we can prove that our calculations yield the
> exact same results in all cases as HWs formula. Covering all scenarios that
> bandwidth calcs covers would be quite an extensive undertaking and I'm sure
> we'd miss important cases.

Is this only going to happen for X86 APUs? Using floating point in the
kernel requires
a lot of care to be taken, are we doing it properly?

Really rewriting the calcs in fixed point is the best option, maybe push back on
the hardware team to have a fixed point version created.

Dave.