Re: [PATCH] drm/i915: Fix DPLL warning when starting guest VM

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

On Mon, Oct 30, 2017 at 04:17:06PM +0800, Zhao, Xinda wrote:
> The warning is occurred in guest VM when trying to get clock in encoder
> initialization.
> 
> intel_modeset_init()
>   ->intel_modeset_setup_hw_state()
>     ->intel_ddi_get_config()
>       ->intel_ddi_clock_get()
>         ->skl_ddi_clock_get()
>           ->intel_get_shared_dpll_id()
>             ->WARN_ON(pll < dev_priv->shared_dplls||
>                 pll > &dev_priv->shared_dplls[dev_priv->num_shared_dpll])
> 
> In encoder initialization, shared DPLL is used for calculating clock for
> DDI ports, but it is not set when crtc is not active.
> In some cases, encoder is enabled while crtc is disabled, during encoder
> initialization, the warning occurred.
> 
> Signed-off-by: Zhao, Xinda <xinda.zhao@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 28c25cb..ef35c12 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1489,6 +1489,16 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
>  			 struct intel_crtc_state *pipe_config)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> +	struct intel_crtc *crtc = to_intel_crtc(pipe_config->base.crtc);
> +
> +	/*
> +	 * For DDI ports we always use a shared PLL.
> +	 * But the shared PLL will not be set when crtc is not active.
> +	 */
> +	if (crtc->active == false) {

Seem to me that the correct fix would be to do the DPLL readout
regardless of the state of the pipe.

> +		DRM_DEBUG_KMS("Trying to get clock, but pipe is not active.\n");
> +		return;
> +	}
>  
>  	if (INTEL_GEN(dev_priv) <= 8)
>  		hsw_ddi_clock_get(encoder, pipe_config);
> -- 
> 2.7.4
> 
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-- 
Ville Syrjälä
Intel OTC
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