[PATCH 1/2] drm/amdgpu: return bo itself if userptr is cpu addr of bo (v3)

[Christian König]

Am 31.07.2018 um 10:58 schrieb Zhang, Jerry (Junwei):
> On 07/31/2018 04:13 PM, Christian König wrote:
>> Am 31.07.2018 um 10:05 schrieb Zhang, Jerry (Junwei):
>>> On 07/31/2018 03:03 PM, Christian König wrote:
>>>> Am 31.07.2018 um 08:58 schrieb Zhang, Jerry (Junwei):
>>>>> On 07/30/2018 06:47 PM, Christian König wrote:
>>>>>> Am 30.07.2018 um 12:02 schrieb Junwei Zhang:
>>>>>> [SNIP]
>>>>>> Please double check if that is still up to date.
>>>>>
>>>>> We may have to replace drm_gem_object_reference() with 
>>>>> drm_gem_object_get().
>>>>>
>>>>> On 2nd thought, do we really need to do reference every time?
>>>>
>>>> Yes, that's a must have. Otherwise the handle could be freed and 
>>>> reused already when we return.
>>>>
>>>>> if UMD find the same gem object for 3 times, it also need to 
>>>>> explicitly free(put) that object for 3 times?
>>>>
>>>> Correct yes. Thinking more about this the real problem is to 
>>>> translate the handle into a structure in libdrm.
>>>>
>>>> Here we are back to the problem Marek and Michel has been working 
>>>> on for a while that we always need to be able to translate a handle 
>>>> into a bo structure.....
>>>>
>>>> So that needs to be solved before we can upstream the changes.
>>>
>>> Thanks for your info.
>>> It's better to fix that before upstream.
>>
>> Thinking more about this the hash currently used in libdrm is not 
>> adequate any more.
>>
>> E.g. we now need to be able to find all BOs based on their handle. 
>> Since the handles are dense either an r/b tree or a radix tree now 
>> sounds like the best approach to me.
>
> Not sure the exact reason that we added hash table in libdrm.

The reason for that was that when a kernel function returns a handle we 
need to make sure that we always use the same struct amdgpu_bo for it.

Otherwise you run into quite some problems with syncing etc...

> But it really costs much less time than calling IOCTL to find BO by 
> their handles.

Well we could just completely drop the kernel implementation and use an 
userspace implementation.

And yes I agree when we need a tree anyway it would probably be faster 
than calling the IOCTL to find the BO.

Christian.

>
> In this case, UMD seems not to be able to get BO handle and try to 
> verify it by cpu address then.
> In another word, UMD would like to find if the memory is created as BO 
> or system memory, I suppose.
>
> Regards,
> Jerry
>
>
>>
>> Christian.
>>
>>>
>>> Regards,
>>> Jerry
>>
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