drm/i915/cnl: Allow 2 pixel per clock on Cannonlake.

This is heavily based on a initial patch provided by Ville
plus all changes provided later by Ander.

As Geminilake, Cannonlake also supports 2 pixels per clock.

Different from Geminilake we are not implementing the 99% Wa.
But we can revisit that decision later if we find out
any limitation on later CNL SKUs.

v2: Rebase on top of commit 'd305e061 ("drm/i915: Track
minimum acceptable cdclk instead of "minimum dotclock")'

v3: When fixing HDMI on CNL I noticed that I missed to convert
    back the doubled pixel rate to cdclk.

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171003223142.26264-1-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_cdclk.c

@@ -1866,12 +1866,7 @@ static int intel_pixel_rate_to_cdclk(struct drm_i915_private *dev_priv,
 				     int pixel_rate)
 {
 	if (INTEL_GEN(dev_priv) >= 10)
-		/*
-		 * FIXME: Switch to DIV_ROUND_UP(pixel_rate, 2)
-		 * once DDI clock voltage requirements are
-		 * handled correctly.
-		 */
-		return pixel_rate;
+		return DIV_ROUND_UP(pixel_rate, 2);
 	else if (IS_GEMINILAKE(dev_priv))
 		/*
 		 * FIXME: Avoid using a pixel clock that is more than 99% of the cdclk
@@ -2188,12 +2183,7 @@ static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv)
 	int max_cdclk_freq = dev_priv->max_cdclk_freq;
 
 	if (INTEL_GEN(dev_priv) >= 10)
-		/*
-		 * FIXME: Allow '2 * max_cdclk_freq'
-		 * once DDI clock voltage requirements are
-		 * handled correctly.
-		 */
-		return max_cdclk_freq;
+		return 2 * max_cdclk_freq;
 	else if (IS_GEMINILAKE(dev_priv))
 		/*
 		 * FIXME: Limiting to 99% as a temporary workaround. See

drivers/gpu/drm/i915/intel_display.c

@@ -12765,7 +12765,7 @@ skl_max_scale(struct intel_crtc *intel_crtc, struct intel_crtc_state *crtc_state
 	crtc_clock = crtc_state->base.adjusted_mode.crtc_clock;
 	max_dotclk = to_intel_atomic_state(crtc_state->base.state)->cdclk.logical.cdclk;
 
-	if (IS_GEMINILAKE(dev_priv))
+	if (IS_GEMINILAKE(dev_priv) || INTEL_GEN(dev_priv) >= 10)
 		max_dotclk *= 2;
 
 	if (WARN_ON_ONCE(!crtc_clock || max_dotclk < crtc_clock))

drivers/gpu/drm/i915/intel_pm.c

@@ -3932,6 +3932,7 @@ skl_pipe_downscale_amount(const struct intel_crtc_state *crtc_state)
 int skl_check_pipe_max_pixel_rate(struct intel_crtc *intel_crtc,
 				  struct intel_crtc_state *cstate)
 {
+	struct drm_i915_private *dev_priv = to_i915(intel_crtc->base.dev);
 	struct drm_crtc_state *crtc_state = &cstate->base;
 	struct drm_atomic_state *state = crtc_state->state;
 	struct drm_plane *plane;
@@ -3974,7 +3975,7 @@ int skl_check_pipe_max_pixel_rate(struct intel_crtc *intel_crtc,
 	crtc_clock = crtc_state->adjusted_mode.crtc_clock;
 	dotclk = to_intel_atomic_state(state)->cdclk.logical.cdclk;
 
-	if (IS_GEMINILAKE(to_i915(intel_crtc->base.dev)))
+	if (IS_GEMINILAKE(dev_priv) || INTEL_GEN(dev_priv) >= 10)
 		dotclk *= 2;
 
 	pipe_max_pixel_rate = div_round_up_u32_fixed16(dotclk, pipe_downscale);