[PATCH] drm/amd/display: Limit DCN to x86 arch
harry.wentland at amd.com
Fri May 19 20:28:44 UTC 2017
On 2017-05-19 04:18 PM, Dave Airlie wrote:
> 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
>> 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?
This case would be only for AMD X86 APUs, although I wouldn't be
surprised if we'd see something similar for discrete ASICs in the future.
Are you aware of anyone using our GPUs on non-X86 architectures? If so,
I never heard of it.
I realize this is raising a lot of concern. I was concerned myself when
I first saw this. Beside calling kernel_fpu_begin() and kernel_fpu_end()
are there other things to watch out for?
> 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.
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