drm/i915: Add quirk to disable SSC on Lenovo U160 LVDS

We've tried several times to make this machine 'just work', but every
patch that does causes many other machines to fail. This adds a quirk
which special cases this hardware and forces ssc to be
disabled. There's no way to override this from the command line; that
would be a significantly more invasive change.

This patch fixes #36656 on fdo bugzilla:
https://bugs.freedesktop.org/show_bug.cgi?id=36656

Signed-off-by: Keith Packard <keithp@keithp.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=36656
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.h

@@ -262,6 +262,7 @@ enum intel_pch {
 };
 
 #define QUIRK_PIPEA_FORCE (1<<0)
+#define QUIRK_LVDS_SSC_DISABLE (1<<1)
 
 struct intel_fbdev;
 

drivers/gpu/drm/i915/intel_display.c

@@ -4305,7 +4305,8 @@ static void intel_update_watermarks(struct drm_device *dev)
 
 static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
 {
-	return dev_priv->lvds_use_ssc && i915_panel_use_ssc;
+	return dev_priv->lvds_use_ssc && i915_panel_use_ssc
+		&& !(dev_priv->quirks & QUIRK_LVDS_SSC_DISABLE);
 }
 
 static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
@@ -7810,6 +7811,15 @@ static void quirk_pipea_force (struct drm_device *dev)
 	DRM_DEBUG_DRIVER("applying pipe a force quirk\n");
 }
 
+/*
+ * Some machines (Lenovo U160) do not work with SSC on LVDS for some reason
+ */
+static void quirk_ssc_force_disable(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	dev_priv->quirks |= QUIRK_LVDS_SSC_DISABLE;
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;
@@ -7838,6 +7848,9 @@ struct intel_quirk intel_quirks[] = {
 	/* 855 & before need to leave pipe A & dpll A up */
 	{ 0x3582, PCI_ANY_ID, PCI_ANY_ID, quirk_pipea_force },
 	{ 0x2562, PCI_ANY_ID, PCI_ANY_ID, quirk_pipea_force },
+
+	/* Lenovo U160 cannot use SSC on LVDS */
+	{ 0x0046, 0x17aa, 0x3920, quirk_ssc_force_disable },
 };
 
 static void intel_init_quirks(struct drm_device *dev)