[PATCH 01/11] drm/vram: Add struct drm_vram_buffer to VRAM helpers

[Thomas Zimmermann]

Hi

Am 19.09.19 um 07:58 schrieb Gerd Hoffmann:
> On Wed, Sep 18, 2019 at 04:22:57PM +0200, Thomas Zimmermann wrote:
>> Drivers with dedicated video memory occasionally need to reserve a memory
>> area for a specific purpose, such as cursor images or sprites. Using GEM
>> VRAM buffer objects can be problematic. For small buffers, GEM VRAM buffer
>> objects are inefficient as they are aligned to page boundaries.
> 
> I would still allocate gem objects for that.  Then use them as pool
> instead of using them directly.
> 
> Not sure this is worth the trouble just for the cursors though as they
> are big enough that page-sized allocations don't waste memory.
> 
>> And they cannot easily be placed at specific memory offsets. This can
>> lead to memory fragmentation and is a problem for hardware with only a
>> small amount of memory.
> 
> Note that there is a flag to change the allocation strategy
> (TTM_PL_FLAG_TOPDOWN).  You could allocate the cursor objects
> with the flag set.  Should be good enough to avoid fragmentation.
> 
> I have a patch doing exactly that for qxl, for the same reason:
> https://git.kraxel.org/cgit/linux/commit/?id=e00e913a64c6fba9630b311f8bc71bd7c9842479
> (no, that patch wasn't sent to the list yet).
> 
> We could do the same for vram and either let the driver explicitly ask
> for top-down allocation, or use some threshold like the qxl patch.
> 
> So, I'm not convinced we actually need the drm_vram_buffer
> infrastructure.

Well, OK. I don't mind using GEM buffers if they can solve the problem.
Half of the patch set is unrelated to VRAM buffers anyway.

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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