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

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

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@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.

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
>>
>