Why so complicated? If old user space compatibility is required, just use 


On 2018-03-07 05:12 AM, Michel Dänzer wrote:
> On 2018-03-07 11:04 AM, Christian König wrote:
>> Am 07.03.2018 um 10:53 schrieb Michel Dänzer:
>>> On 2018-03-07 10:47 AM, Christian König wrote:
>>>> See when I tested this the DDX and Mesa where unmodified, so both still
>>>> assumed VRAM as placement for scanout BOs, but the kernel forced scanout
>>>> BOs into GTT for testing.
>>>> So what happened was that on scanout we moved the VRAM BO to GTT and
>>>> after unpinning it on the first command submission which used the BO we
>>>> moved it back to VRAM again.
>>>> So as long as we don't want a severe performance penalty when you
>>>> combine old userspace with new kernel using a kernel parameter to force
>>>> scanout from GTT is not possible.
>>> That means we either need to come up with a different workaround for
>>> hardware issues transitioning between scanout from VRAM and GTT, or we
>>> can't scan out from GTT in that case.
>> What exactly was the problem with the transition from VRAM to GTT?
>> I mean what we can rather easily do is check where the existing BO is
>> pinned and then always pin into the same domain on page flip.
> Yeah, something like that could work. In which case, all that's needed
> is a way for userspace to know that GTT scanout can work, right? With
> that information, it can manage the domains of scanout BOs as it wants.
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