From ee59792c97176f12c1da31f29fc4c2aab187f06e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Fri, 28 Jan 2022 12:37:50 +0200
Subject: [PATCH] drm/i915: Disable DRRS on IVB/HSW port != A
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Git-commit: ee59792c97176f12c1da31f29fc4c2aab187f06e
Patch-mainline: v5.17-rc4
Alt-commit: f0d4ce59f4d48622044933054a0e0cefa91ba15e
References: git-fixes

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/display/intel_drrs.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/gpu/drm/i915/display/intel_drrs.c
+++ b/drivers/gpu/drm/i915/display/intel_drrs.c
@@ -445,6 +445,7 @@ intel_dp_drrs_init(struct intel_connecto
 		   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_edp_drrs_downclock_work);
@@ -456,6 +457,13 @@ intel_dp_drrs_init(struct intel_connecto
 		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;