When the modeset code is reached with a CRTC that only needs a flip, the
code that assigns PLLs is skipped. But since there is still a state swap
for that CRTC, the current PLL assignment needs to be preserved. I
missed the ddi_pll_sel field in the following commit, which causes
warnings in DDI platforms.
commit 
4978cc93d9ac240b435ce60431aef24239b4c270
Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Date:   Tue Apr 21 17:13:21 2015 +0300
    drm/i915: Preserve shared DPLL information in new pipe_config
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90410
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
 
        struct intel_crtc_scaler_state scaler_state;
        struct intel_dpll_hw_state dpll_hw_state;
        enum intel_dpll_id shared_dpll;
+       uint32_t ddi_pll_sel;
 
        /* Clear only the intel specific part of the crtc state excluding scalers */
        tmp_state = crtc_state->base;
        scaler_state = crtc_state->scaler_state;
        shared_dpll = crtc_state->shared_dpll;
        dpll_hw_state = crtc_state->dpll_hw_state;
+       ddi_pll_sel = crtc_state->ddi_pll_sel;
 
        memset(crtc_state, 0, sizeof *crtc_state);
 
        crtc_state->scaler_state = scaler_state;
        crtc_state->shared_dpll = shared_dpll;
        crtc_state->dpll_hw_state = dpll_hw_state;
+       crtc_state->ddi_pll_sel = ddi_pll_sel;
 }
 
 static int