Re: [PATCH 1/2] drm/ttm: cleanup and add TTM_PL_FLAG_TEMPORARY

["Thomas Hellström (Intel)" <thomas_os@shipmail.org>]

Hi, Lang,

On 5/31/21 10:19 AM, Yu, Lang wrote:
> [Public]
>
>> Hi,
>> On 5/27/21 3:30 AM, Lang Yu wrote:
>>> Make TTM_PL_FLAG_* start from zero and add
>>> TTM_PL_FLAG_TEMPORARY flag for temporary
>>> GTT allocation use.
>> GTT is a driver private acronym, right? And it doesn't look like
>> TTM_PL_FLAG_TEMPORARY will be used in core TTM, so should we instead set
>> aside a mask in the PL flag for driver-private use?
> Hi Thomas,
>
> Thanks for your comments and advice, GTT means Graphics Translation Table here, seems
> a general acronym. TTM_PL_FLAG_TEMPORARY may also be used by other drives.
> I have made other patches for this. Please help review.
>
> Regards,
> Lang
>
My point was really that the flag naming and documentation should 
reflect what core ttm is doing with that flag. If there is no specific 
core TTM usage, IMO we should move it to a driver specific flag to avoid 
future confusion. In particular a writer of a generic TTM resource 
manager should be able to know without looking at an old commit message 
what the placement flag is intended for.

So here we add a flag where core TTM forces a bo move on validate and 
that's it. And that appears to be how it's used when an amdgpu bo is 
evicted to GTT, (btw should it be accounted in this situation?)

The other use is to force the amdgpu driver to temporarily accept it 
into GTT when there is a lack of space, and IMHO that's a driver 
specific use and we should allocate a mask for driver specific flags for 
that.

So shouldn't this be two flags, really?

TTM_PL_FLAG_FORCE_MOVE

and

AMDGPU_PL_FLAG_TEMPORARY

Thanks,

/Thomas

>> Thomas
>> -----Original Message-----
>> From: Yu, Lang <Lang.Yu@amd.com>
>> Sent: Thursday, May 27, 2021 9:31 AM
>> To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>> Cc: Koenig, Christian <Christian.Koenig@amd.com>; Huang, Ray
>> <Ray.Huang@amd.com>; Deucher, Alexander <Alexander.Deucher@amd.com>;
>> Yu, Lang <Lang.Yu@amd.com>
>> Subject: [PATCH 1/2] drm/ttm: cleanup and add TTM_PL_FLAG_TEMPORARY
>>
>> Make TTM_PL_FLAG_* start from zero and add TTM_PL_FLAG_TEMPORARY flag
>> for temporary GTT allocation use.
>>
>> Signed-off-by: Lang Yu <Lang.Yu@amd.com>
>> ---
>> include/drm/ttm/ttm_placement.h | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/drm/ttm/ttm_placement.h
>> b/include/drm/ttm/ttm_placement.h index aa6ba4d0cf78..9f5cfc7c2d5a 100644
>> --- a/include/drm/ttm/ttm_placement.h
>> +++ b/include/drm/ttm/ttm_placement.h
>> @@ -47,8 +47,9 @@
>>   * top of the memory area, instead of the bottom.
>>   */
>>
>> -#define TTM_PL_FLAG_CONTIGUOUS  (1 << 19)
>> -#define TTM_PL_FLAG_TOPDOWN     (1 << 22)
>> +#define TTM_PL_FLAG_CONTIGUOUS  (1 << 0)
>> +#define TTM_PL_FLAG_TOPDOWN     (1 << 1)
>> +#define TTM_PL_FLAG_TEMPORARY   (1 << 2)
>>
>> /**
>>   * struct ttm_place
>> --
>> 2.25.1