Re: [PATCH] drm/i915: Keep physical cursors pinned while in use

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Aug 17, 2018 at 09:24:05AM +0100, Chris Wilson wrote:
> The optimisation inherent in commit 6a2c4232ece1 ("drm/i915: Make the
> physical object coherent with GTT") relies on that once we allocated a
> cursor we would have coherent, zero overhead access to the scanout plane
> holding the cursor. That is we could then do the very frequent cursor
> updates X enjoys with no indirection or kernel involvement. However,
> that all hinges on the GGTT mmap of the cursor being pinned and not
> require refaulting on each access -- handling such a page fault likely
> requires the busy GGTT to be rearranged causing a stall. A very simple
> fix is then to handle the physical cursor exactly like other cursors and
> keep its vma pinned while active.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107600

I guess this wasn't the thing we wanted. But seems quite harmless to
me anyway, so 

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

in case you still want to land it.

> References: 6a2c4232ece1 ("drm/i915: Make the physical object coherent with GTT")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 592b847db88e..d47ec9fd4af4 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12966,8 +12966,11 @@ static int intel_plane_pin_fb(struct intel_plane_state *plane_state)
>  	    INTEL_INFO(dev_priv)->cursor_needs_physical) {
>  		struct drm_i915_gem_object *obj = intel_fb_obj(fb);
>  		const int align = intel_cursor_alignment(dev_priv);
> +		int err;
>  
> -		return i915_gem_object_attach_phys(obj, align);
> +		err = i915_gem_object_attach_phys(obj, align);
> +		if (err)
> +			return err;
>  	}
>  
>  	vma = intel_pin_and_fence_fb_obj(fb,
> -- 
> 2.18.0

-- 
Ville Syrjälä
Intel
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