drm/i915: Disable DRRS on IVB/HSW port != A

Currently we allow DRRS on IVB PCH ports, but we're missing a
few programming steps meaning it is guaranteed to not work.
And on HSW DRRS is not supported on anything but port A ever
as only transcoder EDP has the M2/N2 registers (though I'm
not sure if HSW ever has eDP on any other port).

Starting from BDW all transcoders have the dynamically
reprogrammable M/N registers so DRRS could work on any
port.

Stop initializing DRRS on ports where it cannot possibly work.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128103757.22461-11-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit f0d4ce59f4d48622044933054a0e0cefa91ba15e)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_drrs.c b/drivers/gpu/drm/i915/display/intel_drrs.c
index c1439fc..3ff149d 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_drrs.c
+++ b/drivers/gpu/drm/i915/display/intel_drrs.c
@@ -405,6 +405,7 @@ intel_drrs_init(struct intel_connector *connector,
                struct drm_display_mode *fixed_mode)
 {
        struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
+       struct intel_encoder *encoder = connector->encoder;
        struct drm_display_mode *downclock_mode = NULL;
 
        INIT_DELAYED_WORK(&dev_priv->drrs.work, intel_drrs_downclock_work);
@@ -416,6 +417,13 @@ intel_drrs_init(struct intel_connector *connector,
                return NULL;
        }
 
+       if ((DISPLAY_VER(dev_priv) < 8 && !HAS_GMCH(dev_priv)) &&
+           encoder->port != PORT_A) {
+               drm_dbg_kms(&dev_priv->drm,
+                           "DRRS only supported on eDP port A\n");
+               return NULL;
+       }
+
        if (dev_priv->vbt.drrs_type != SEAMLESS_DRRS_SUPPORT) {
                drm_dbg_kms(&dev_priv->drm, "VBT doesn't support DRRS\n");
                return NULL;