Re: [Intel-gfx] [v2] drm/i915/display: Add an extra vblank wait before fbc activation

[Anshuman Gupta <anshuman.gupta@intel.com>]

On 2020-08-17 at 16:55:29 +0530, Uma Shankar wrote:
> Add an extra vblank before fbc is activated.
> WA: 1409689360
> Corruption with FBC around plane 1A enabling. In the Frame Buffer
> Compression programming sequence "Display Plane Enabling with FBC"
> add a wait for vblank between plane enabling step 1 and FBC enabling
> step 2.
> 
> v2: Add wait only for active crtc
> 
> Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fbc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index 2ab32e6532ff..2a9d4796c4a8 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -1085,10 +1085,13 @@ static void __intel_fbc_post_update(struct intel_crtc *crtc)
>  	if (!intel_fbc_can_activate(crtc))
>  		return;
>  
> -	if (!fbc->busy_bits)
> +	if (!fbc->busy_bits) {
> +		if (IS_TIGERLAKE(dev_priv))
> +			intel_wait_for_vblank_if_active(dev_priv, crtc->pipe);
IMHO with this we are also adding a VBLANK wait when fbc is getting enabled
from frontbuffer flush flow intel_fbc_flush(), i am being afraid if there 
could be unnecessary VBLANK wait here.
Thanks,
Anshuman Gupta.
>  		intel_fbc_hw_activate(dev_priv);
> -	else
> +	} else {
>  		intel_fbc_deactivate(dev_priv, "frontbuffer write");
> +	}
>  }
>  
>  void intel_fbc_post_update(struct intel_atomic_state *state,
> -- 
> 2.22.0
> 
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