drm/i915: Add debug module option for VTd validation

VTd has a few too many "outright disable the damn thing" workarounds
accumulated and for validation we want a simple knob to make sure we
disable them all.

Since this is for bdw+ validation and atm we don't have any
workarounds for bdw this option currently does nothing. So currently
this is just a placeholder to make sure reality will match with the
documented process for our validation people.

v2: Fix up param description (Jani).

v3: Actually git add ...

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1923,6 +1923,7 @@ struct i915_params {
 	bool prefault_disable;
 	bool reset;
 	bool disable_display;
+	bool disable_vtd_wa;
 };
 extern struct i915_params i915 __read_mostly;
 

drivers/gpu/drm/i915/i915_params.c

@@ -47,6 +47,7 @@ struct i915_params i915 __read_mostly = {
 	.invert_brightness = 0,
 	.disable_display = 0,
 	.enable_cmd_parser = 1,
+	.disable_vtd_wa = 0,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -149,6 +150,9 @@ MODULE_PARM_DESC(invert_brightness,
 module_param_named(disable_display, i915.disable_display, bool, 0600);
 MODULE_PARM_DESC(disable_display, "Disable display (default: false)");
 
+module_param_named(disable_vtd_wa, i915.disable_vtd_wa, bool, 0600);
+MODULE_PARM_DESC(disable_vtd_wa, "Disable all VT-d workarounds (default: false)");
+
 module_param_named(enable_cmd_parser, i915.enable_cmd_parser, int, 0600);
 MODULE_PARM_DESC(enable_cmd_parser,
 		 "Enable command parsing (1=enabled [default], 0=disabled)");