[PATCH 39/49] drm/ttm: make ttm_bo_man_init/takedown take type + args

[Christian König]

Am 06.08.20 um 05:46 schrieb Dave Airlie:
>> That was not what I was talking about. Take a look at what those fields
>> are used for :)
>>
>>
>> As far as I see the only usage of the size is in
>> ttm_resource_manager_debug(). But this size is actually totally opaque
>> to TTM, it could be pages, bytes, fried chicken wings or whatever. In
>> other words it would be much better to print it in the debug callback of
>> each resource manager.
> Size is a bit trickier as the drivers use in a couple of funky places, radeon
> pokes inside the range manager and adjust its size post init, and amdgpu
> uses size to validate a bunch of bo sizing. These shouldn't be too messy to
> workaround.

Yeah, I already wanted o clean that up in radeon for years now :)

Amdgpu should be easy to fix, most likely we just don't store the gtt 
size anywhere else.

But yes, those are TTM internals which drivers should not touch.

>> The available_caching is completely superfluous as well. The original
>> idea what that a driver could specify multiple placements as flags in
>> one entry, but no driver ever used that as far as I know and it became
>> completely deprecated in 2014 when I moved the lpfn and fpfn into each
>> place.
>>
>>
>> The default_caching is used in ttm_bo_select_caching(), but this is
>> complete utterly nonsense. It just results in multiple possible cache
>> behaviors being selected, which are then fortunately ignored by
>> ttm_tt_set_placement_caching :)
>>
>>
>> To be honest I think just removing those parameters and the associated
>> caching flags all together is the next logical step.
> Definitely something to burn down alright.

IIRC we have a bit of dead AGP code in radeon which still tries to use this.

Nouveau might have something as well, going to take a look now.

But in general I think that drivers should just say I want caching X for 
this BO instead of TTM making an educated guess based on some flags set 
in different places.

Christian.

>
> Dave.