[Intel-gfx] [PATCH 12/12] drm/i915: Suppress spurious underruns on gen2

[Souza, Jose]

On Wed, 2020-04-29 at 13:10 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Often we seem to detect an underrun right after modeset on gen2.
> It seems to be a spurious detection (potentially the pipe is still
> in a wonky state when we enable the planes). An extra vblank wait
> seems to cure it.

Reviewed-by: José Roberto de Souza <jose.souza at intel.com>

> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index a0d1057d75ee..f330054e64c5 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -7517,6 +7517,10 @@ static void i9xx_crtc_enable(struct intel_atomic_state *state,
>  	intel_crtc_vblank_on(new_crtc_state);
>  
>  	intel_encoders_enable(state, crtc);
> +
> +	/* prevents spurious underruns */
> +	if (IS_GEN(dev_priv, 2))
> +		intel_wait_for_vblank(dev_priv, pipe);
>  }
>  
>  static void i9xx_pfit_disable(const struct intel_crtc_state *old_crtc_state)