Deprecation of AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED

[Christian König]

Am 30.06.2017 um 09:14 schrieb Michel Dänzer:
> On 30/06/17 03:59 PM, Christian König wrote:
>> Am 30.06.2017 um 08:51 schrieb Michel Dänzer:
>>> We can deal with that internally in the kernel, while fixing the
>>> existing flag for userspace.
>> And as I said, NAK to that approach. I'm not going to add a
>> CPU_ACCESS_REALLY_REQUIRED flag in the kernel just because mesa has
>> messed up it's use case.
>>
>> We could agree on filtering that flag from userspace when BOs are
>> created and/or map it to a CREATE_CPU_ACCESS_HINT flag.
> Then I propose the following:
>
> One patch:
>
> Convert AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED to a kernel internal flag
> AMDGPU_GEM_CPU_ACCESS_HINT in amdgpu_gem_create_ioctl, which is
> initially treated the same way as AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED.
>
> Another patch:
>
> Change the treatment of AMDGPU_GEM_CPU_ACCESS_HINT according to John's
> patch 4 in the latest series, or a variation of that as discussed on IRC.
>
>
> If any regressions are reported, we will be able to differentiate
> whether they are due to the addition of the new flag itself or due to
> the change in its handling.


It just occurred to me that there is a simpler way of handling this: We 
just never clear the flag on kernel allocations.

See my main concern are the in kernel users of the flag which use it as 
guarantee that the BO is CPU accessible.

If we handle those specially there shouldn't be a problem clearing the 
flag for the UMD BOs.

Christian.