[PATCH v2 13/15] drm/ttm: Add BO and offset arguments for vm_access and vm_fault ttm handlers.

[Christian König]

Am 18.05.21 um 17:25 schrieb Thomas Hellström:
>
> On 5/18/21 5:17 PM, Christian König wrote:
>>
>>
>> Am 18.05.21 um 17:11 schrieb Thomas Hellström:
>>>
>>> On 5/18/21 5:07 PM, Christian König wrote:
>>>> Am 18.05.21 um 16:55 schrieb Thomas Hellström:
>>>>> From: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>>>>
>>>>> This allows other drivers that may not setup the vma in the same way
>>>>> to use the ttm bo helpers.
>>>>
>>>> Uff can you please explain why exactly you need that?
>>>>
>>>> Providing the BO is not much of a problem, but having the BO at 
>>>> different VMA offsets is really a no-go with TTM.
>>>>
>>>> Christian.
>>>
>>> The current i915 uapi is using different offsets for different 
>>> caching :/. We're currently working around that by using 
>>> ttm_bo_type_kernel (no TTM vma offset at all) and i915's offset.
>>
>> Can you instead adjust the offset in the mmap callback like we do for 
>> dma-buf?
> Will have to take a look.
>>
>> That's really a no-go what you describe here because it will mess up 
>> reverse mapping lockup for buffer movement.
>
> You mean the unmap_mapping_range() stuff? That's not a problem since 
> it's a NOP for kernel ttm buffers, and the i915 move() / swap_notify() 
> takes care of killing the ptes.

That design is a certain NAK from my side for upstreaming this.

PTE handling is the domain of TTM, drivers should never mess with that 
directly.

Christian.

>
> While we're in the process of killing that offset flexibility for 
> discrete, we can't do so for older hardware unfortunately.
>
> /Thomas
>
>
>>
>> Christian.
>
>
>
>>
>>>
>>> /Thomas
>>>
>>