drm/i915: constify fdi link training vtable

Put the vtable into ro memory.
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ec4687956f9b98024fea55b2f0ed1e192e244ff1.1632869550.git.jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_fdi.c

@@ -15,7 +15,7 @@ void intel_fdi_link_train(struct intel_crtc *crtc,
 {
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 
-	dev_priv->fdi_funcs.fdi_link_train(crtc, crtc_state);
+	dev_priv->fdi_funcs->fdi_link_train(crtc, crtc_state);
 }
 
 /* units of 100MHz */
@@ -1013,15 +1013,27 @@ void lpt_fdi_program_mphy(struct drm_i915_private *dev_priv)
 	intel_sbi_write(dev_priv, 0x21EC, tmp, SBI_MPHY);
 }
 
+static const struct intel_fdi_funcs ilk_funcs = {
+	.fdi_link_train = ilk_fdi_link_train,
+};
+
+static const struct intel_fdi_funcs gen6_funcs = {
+	.fdi_link_train = gen6_fdi_link_train,
+};
+
+static const struct intel_fdi_funcs ivb_funcs = {
+	.fdi_link_train = ivb_manual_fdi_link_train,
+};
+
 void
 intel_fdi_init_hook(struct drm_i915_private *dev_priv)
 {
 	if (IS_IRONLAKE(dev_priv)) {
-		dev_priv->fdi_funcs.fdi_link_train = ilk_fdi_link_train;
+		dev_priv->fdi_funcs = &ilk_funcs;
 	} else if (IS_SANDYBRIDGE(dev_priv)) {
-		dev_priv->fdi_funcs.fdi_link_train = gen6_fdi_link_train;
+		dev_priv->fdi_funcs = &gen6_funcs;
 	} else if (IS_IVYBRIDGE(dev_priv)) {
 		/* FIXME: detect B0+ stepping and use auto training */
-		dev_priv->fdi_funcs.fdi_link_train = ivb_manual_fdi_link_train;
+		dev_priv->fdi_funcs = &ivb_funcs;
 	}
 }

drivers/gpu/drm/i915/i915_drv.h

@@ -991,7 +991,7 @@ struct drm_i915_private {
 	struct intel_hotplug_funcs hotplug_funcs;
 
 	/* fdi display functions */
-	struct intel_fdi_funcs fdi_funcs;
+	const struct intel_fdi_funcs *fdi_funcs;
 
 	/* display pll funcs */
 	struct intel_dpll_funcs dpll_funcs;