drm/i915: robustify edp_pll_on/off

With the previous patch to clean up where exactly these two functions
are getting called, this patch can tackle the enable/disable code
itself:

- WARN if the port enable bit is in the wrong state or if the edp pll
  bit is in the wrong state, just for paranoia's sake.
- Don't disable the edp pll harder in the modeset functions just for
  fun.
- Don't set the edp pll enable flag in intel_dp->DP in modeset, do
  that while changing the actual hw state. We do the same with the
  actual port enable bit, so this is a bit more consistent.
- Track the current DP register value when setting things up and add
  some comments how intel_dp->DP is used in the disable code.

v2: Be more careful with resetting intel_dp->DP - otherwise dpms
off->on will fail spectacularly, becuase we enable the eDP port when
we should only enable the eDP pll.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 18 insertions, 11 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fccc82970ae0..0f8480037cf0 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -887,7 +887,6 @@ intel_dp_mode_set(struct drm_encoder *encoder, struct drm_display_mode *mode,
                 intel_dp->DP |= intel_crtc->pipe << 29;
 
                 /* don't miss out required setting for eDP */
-                intel_dp->DP |= DP_PLL_ENABLE;
                 if (adjusted_mode->clock < 200000)
                         intel_dp->DP |= DP_PLL_FREQ_160MHZ;
                 else
@@ -909,7 +908,6 @@ intel_dp_mode_set(struct drm_encoder *encoder, struct drm_display_mode *mode,
 
                 if (is_cpu_edp(intel_dp)) {
                         /* don't miss out required setting for eDP */
-                        intel_dp->DP |= DP_PLL_ENABLE;
                         if (adjusted_mode->clock < 200000)
                                 intel_dp->DP |= DP_PLL_FREQ_160MHZ;
                         else
@@ -1192,8 +1190,15 @@ static void ironlake_edp_pll_on(struct intel_dp *intel_dp)
 
         DRM_DEBUG_KMS("\n");
         dpa_ctl = I915_READ(DP_A);
-        dpa_ctl |= DP_PLL_ENABLE;
-        I915_WRITE(DP_A, dpa_ctl);
+        WARN(dpa_ctl & DP_PLL_ENABLE, "dp pll on, should be off\n");
+        WARN(dpa_ctl & DP_PORT_EN, "dp port still on, should be off\n");
+
+        /* We don't adjust intel_dp->DP while tearing down the link, to
+         * facilitate link retraining (e.g. after hotplug). Hence clear all
+         * enable bits here to ensure that we don't enable too much. */
+        intel_dp->DP &= ~(DP_PORT_EN | DP_AUDIO_OUTPUT_ENABLE);
+        intel_dp->DP |= DP_PLL_ENABLE;
+        I915_WRITE(DP_A, intel_dp->DP);
         POSTING_READ(DP_A);
         udelay(200);
 }
@@ -1209,6 +1214,13 @@ static void ironlake_edp_pll_off(struct intel_dp *intel_dp)
                              to_intel_crtc(crtc)->pipe);
 
         dpa_ctl = I915_READ(DP_A);
+        WARN((dpa_ctl & DP_PLL_ENABLE) == 0,
+             "dp pll off, should be on\n");
+        WARN(dpa_ctl & DP_PORT_EN, "dp port still on, should be off\n");
+
+        /* We can't rely on the value tracked for the DP register in
+         * intel_dp->DP because link_down must not change that (otherwise link
+         * re-training will fail. */
         dpa_ctl &= ~DP_PLL_ENABLE;
         I915_WRITE(DP_A, dpa_ctl);
         POSTING_READ(DP_A);
@@ -1893,13 +1905,6 @@ intel_dp_link_down(struct intel_dp *intel_dp)
 
         DRM_DEBUG_KMS("\n");
 
-        if (is_edp(intel_dp)) {
-                DP &= ~DP_PLL_ENABLE;
-                I915_WRITE(intel_dp->output_reg, DP);
-                POSTING_READ(intel_dp->output_reg);
-                udelay(100);
-        }
-
         if (HAS_PCH_CPT(dev) && (IS_GEN7(dev) || !is_cpu_edp(intel_dp))) {
                 DP &= ~DP_LINK_TRAIN_MASK_CPT;
                 I915_WRITE(intel_dp->output_reg, DP | DP_LINK_TRAIN_PAT_IDLE_CPT);
@@ -2443,6 +2448,8 @@ intel_dp_init(struct drm_device *dev, int output_reg, enum port port)
 
         intel_dp->output_reg = output_reg;
         intel_dp->port = port;
+        /* Preserve the current hw state. */
+        intel_dp->DP = I915_READ(intel_dp->output_reg);
 
         intel_connector = kzalloc(sizeof(struct intel_connector), GFP_KERNEL);
         if (!intel_connector) {