Re: [PATCH] drm/nouveau: do not move buffers when not needed

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On Mon, Jul 15, 2013 at 6:39 PM, Maarten Lankhorst
<maarten.lankhorst@xxxxxxxxxxxxx> wrote:
> Op 15-07-13 08:05, Ben Skeggs schreef:
>> On Fri, Jul 12, 2013 at 10:45 PM, Maarten Lankhorst
>> <maarten.lankhorst@xxxxxxxxxxxxx> wrote:
>>> I have no idea what this bogus restriction on placement is, but it breaks decoding 1080p
>>> VDPAU at boot speed. With this patch applied I only need to bump the vdec clock to
>>> get real-time 1080p decoding. It prevents a lot of VRAM <-> VRAM buffer moves.
>> It's not bogus, and is required for pre-GF8 boards with VRAM > BAR size.
>>
>> What configuration does the buffer that's getting moved here have
>> exactly?  The placement restriction isn't necessary on GF8, the rest
>> of the restrictions may currently be required still however.
>>
>>= vdpau on NVC0 with tiling. I upload the raw bitstream to a tiling bo. This is ok because
> the vm hides all the tiling translations, and the engines will read the raw bitstream correctly.
Why would you be doing such a thing in the first place?  It seems
pointless, and quite possibly counter-productive to use a tiled layout
for a linear data structure...

> 8<---
> This prevents buffer moves from being done on NV50+, where remapping is not needed because
> the bar has its own VM, instead of only having the first BAR1-size chunk of VRAM accessible.
> nouveau_bo_tile_layout is always 0 on < NV_50.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
> ---
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index d506da5..762bfcd 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -1346,14 +1361,13 @@ nouveau_ttm_fault_reserve_notify(struct ttm_buffer_object *bo)
>         struct nouveau_device *device = nv_device(drm->device);
>         u32 mappable = pci_resource_len(device->pdev, 1) >> PAGE_SHIFT;
>
> -       /* as long as the bo isn't in vram, and isn't tiled, we've got
> -        * nothing to do here.
> +       /*
> +        * if the bo is not in vram, or remapping can be done (nv50+)
> +        * do not worry about placement, any location is valid
>          */
> -       if (bo->mem.mem_type != TTM_PL_VRAM) {
> -               if (nv_device(drm->device)->card_type < NV_50 ||
> -                   !nouveau_bo_tile_layout(nvbo))
> -                       return 0;
> -       }
> +       if (nv_device(drm->device)->card_type >= NV_50 ||
> +           bo->mem.mem_type != TTM_PL_VRAM)
> +               return 0;
I get what you're trying to do here, and we should definitely avoid
the "mappable vram" check on GF8, but I suspect this condition is too
broad.  I'll think about it more after I finish reviewing the rest of
the patches on the list..

Thanks,
Ben.
>
>         /* make sure bo is in mappable vram */
>         if (bo->mem.start + bo->mem.num_pages < mappable)
>
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