[PATCH libdrm 1/2] amdgpu: prevent an integer wraparound of cpu_map_count

[Koenig, Christian]

Am 30.10.18 um 16:59 schrieb Michel Dänzer:
> On 2018-10-30 4:52 p.m., Marek Olšák wrote:
>> On Tue, Oct 30, 2018, 11:49 AM Marek Olšák <maraeo at gmail.com> wrote:
>>> On Tue, Oct 30, 2018, 4:20 AM Michel Dänzer <michel at daenzer.net> wrote:
>>>
>>>> On 2018-10-29 10:15 p.m., Marek Olšák wrote:
>>>>> You and I discussed this extensively internally a while ago. It's
>>>> expected
>>>>> and correct behavior. Mesa doesn't unmap some buffers and never will.
>>>> It doesn't need to keep mapping the same buffer over and over again
>>>> though, does it?
>>>>
>>> It doesnt map it again. It just doesnt unmap. So the next map call just
>>> returns the pointer. It's correct to stop the counter wraparound.
>>>
>> Mesa doesn't track whether a buffer is already mapped. Libdrm tracks that.
>> It's a feature of libdrm to return the same pointer and expect infinite
>> number of map calls.
> That's not what the reference counting in libdrm is intended for. It's
> for keeping track of how many independent callers have mapped the
> buffer. Mesa should remember that it mapped a buffer and not map it again.

Well if Mesa just wants to query the existing mapping then why not add a 
amdgpu_bo_get_cpu_ptr() which just queries if a CPU mapping exists and 
if yes returns the appropriate pointer or NULL otherwise?

I mean when we want to abstract everything in libdrm then we just need 
to add the functions we need to use this abstraction.

Christian.