Re: [Intel-gfx] [PATCH 1/2] drm/i915/display/fbc: Make fences a nice-to-have for GEN9+

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

On Tue, Jan 28, 2020 at 03:52:40PM -0800, José Roberto de Souza wrote:
> dGFX have local memory so it do not have aperture and do not support
> CPU fences but even for iGFX it have a small number of fences.
> 
> As replacement for fences to track frontbuffer modifications by CPU
> we have a software tracking that is already in used by FBC and PSR.
> PSR don't support fences so it shows that this tracking is reliable.
> 
> So lets make fences a nice-to-have to activate FBC for GEN9+(as we
> only have a good CI coverage for GEN9+), this will allow us to enable
> FBC for dGFXs and iGFXs even when there is no available fence.
> 
> intel_fbc_hw_tracking_covers_screen() maybe can also have the same
> treatment as fences but BSpec is not clear if the size limitation is
> for hardware tracking or general use of FBC and I don't have a 5K
> display to test it, so keeping as is for safety.
> 
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fbc.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index 2a3f1333c8ff..1f0d24a1dec1 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -717,11 +717,15 @@ static bool intel_fbc_can_activate(struct intel_crtc *crtc)
>  		return false;
>  	}
>  
> -	/* The use of a CPU fence is mandatory in order to detect writes
> -	 * by the CPU to the scanout and trigger updates to the FBC.
> +	/* The use of a CPU fence is one of two ways to detect writes by the
> +	 * CPU to the scanout and trigger updates to the FBC.
> +	 *
> +	 * The other method is by software tracking(see
> +	 * intel_fbc_invalidate/flush()), it will manually notify FBC and nuke
> +	 * the current compressed buffer and recompress it.
>  	 *
>  	 * Note that is possible for a tiled surface to be unmappable (and
> -	 * so have no fence associated with it) due to aperture constaints
> +	 * so have no fence associated with it) due to aperture constraints
>  	 * at the time of pinning.
>  	 *
>  	 * FIXME with 90/270 degree rotation we should use the fence on
> @@ -730,7 +734,7 @@ static bool intel_fbc_can_activate(struct intel_crtc *crtc)
>  	 * For now this will effecively disable FBC with 90/270 degree
>  	 * rotation.
>  	 */
> -	if (cache->fence_id < 0) {
> +	if (cache->fence_id < 0 && INTEL_GEN(dev_priv) < 9) {

Not enough. We need to check that the tiling format is actually supported.
Also the tracking stuff is busted in intel ddx so need to get
https://patchwork.freedesktop.org/series/70636/ merged somehow.

>  		fbc->no_fbc_reason = "framebuffer not tiled or fenced";
>  		return false;
>  	}
> -- 
> 2.25.0
> 
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-- 
Ville Syrjälä
Intel
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