[PATCH 2/2] drm/vram-helper: Alternate between bottom-up and top-down placement

[Thomas Zimmermann]

Hi Gerd

Am 24.04.20 um 11:38 schrieb Gerd Hoffmann:
>   Hi,
> 
>> At some point one has to choose to switch to top-down, and then back
>> again at one of the next BOs. So the current patch effectively splits
>> vram into a lower half and an upper half and puts BOs in alternating halves.
> 
> Hmm, so maybe just make the split explicit instead of playing tricks
> with top_bottom?  Register the lower vram half as TT_VRAM, register the
> upper half as TT_PRIV.  That'll make sure you never have a big
> allocation in the middle blocking things.  Or maybe add a allocation
> strategy flag to ttm which effectively does the same.

It's not that easy. Current cursors n ast are statically allocated. As
soon as you add dynamic cursors into the mix, you'd get OOMs. If the
framebuffer BO goes into VRAM and the cursor BO goes into PRIV, pinning
the next framebuffer BO during a pageflip would send it to VRAM. But
VRAM is still filled with the first framebuffer BO. So the memory
manager needs some flexibility with the placement. Handling all that is
already TTM's job.

I'm preparing v2 of this patch set. It'll get static cursors out of the
way and make the feature opt-in.

Best regards
Thomas

> 
> take care,
>   Gerd
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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