Re: [PATCH] drm/i915: Fallback to using unmappable memory for scanout

[Deepak S <deepak.s@linux.intel.com>]

On Thursday 19 March 2015 03:38 AM, Chris Wilson wrote:
> The existing ABI says that scanouts are pinned into the mappable region
> so that legacy clients (e.g. old Xorg or plymouthd) can write directly
> into the scanout through a GTT mapping. However if the surface does not
> fit into the mappable region, we are better off just trying to fit it
> anywhere and hoping for the best. (Any userspace that is cappable of
> using ginormous scanouts is also likely not to rely on pure GTT
> updates.) In the future, there may even be a kernel mediated method for
> the legacy clients.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Satyanantha, Rama Gopal M <rama.gopal.m.satyanantha@intel.com>
> Cc: Deepak S <deepak.s@linux.intel.com>
> Cc: Damien Lespiau <damien.lespiau@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 9e498e0bbf22..9a1de848e450 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4034,10 +4034,15 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>   
>   	/* As the user may map the buffer once pinned in the display plane
>   	 * (e.g. libkms for the bootup splash), we have to ensure that we
> -	 * always use map_and_fenceable for all scanout buffers.
> +	 * always use map_and_fenceable for all scanout buffers. However,
> +	 * it may simply be too big to fit into mappable, in which case
> +	 * put it anyway and hope that userspace can cope (but always first
> +	 * try to preserve the existing ABI).
>   	 */
>   	ret = i915_gem_obj_ggtt_pin(obj, alignment, PIN_MAPPABLE);
>   	if (ret)
> +		ret = i915_gem_obj_ggtt_pin(obj, alignment, 0);
> +	if (ret)
>   		goto err_unpin_display;
>   

Hi Chris,

if we map the object into unmappable region. I think we should skip fence create ?

Thanks
Deepak

>   	i915_gem_object_flush_cpu_write_domain(obj);

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