[PATCH v4 01/19] drm: Add |struct drm_gem_vram_object| and helpers

[Thomas Zimmermann]

Hi

Am 06.05.19 um 15:17 schrieb Gerd Hoffmann:
>   Hi,
> 
>> This misses the call to drm_gem_vram_placement(), where
>> drm_gem_vram_push_to_system() enforces placement in system memory.
> 
> Ah, missed that detail.
> 
>> We
>> could build a common implementation out of both interfaces, but that
>> would obfuscate the code IMHO. I'd just leave it as it is.
> 
> Ok.
> 
>>>> +struct drm_gem_vram_object {
>>>> +	/* Supported placements are %TTM_PL_VRAM and %TTM_PL_SYSTEM */
>>>> +	struct ttm_placement placement;
>>>> +	struct ttm_place placements[3];
>>>
>>> placements[2] should be enough I guess?
>>
>> TTM_PL_VRAM has index 2 and TTM_PL_SYSTEM has index 0. There's TTM_PL_TT
>> at index 1. We don't use all three array entries here, but I'm not sure
>> if something in TTM does. I took the line from the drivers and didn't
>> change it for that reason.
> 
> TTM_PL_* isn't an index into that array.  See drm_gem_vram_placement()
> which fills that array.  It'll use one or two entries of that array.

The field 'placements' is assigned to 'placement.placements' and
'placement.busy_placement'. The placement field is later given to
ttm_bo_validate() for internal use by TTM. From reading ttm_bo.c, that's
apparently not a problem. I'm just being defensive here, but let's
remove the additional entry if it's just overhead.

Best regards
Thomas


> cheers,
>   Gerd
> 
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-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)

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