drm/i915/guc/slpc: Check GuC status before freq boost

It's possible that i915 might get wedged between a boost
and un-boost. Validate the i915-GuC connection before trying
to send a H2G to change the min frequency.

Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/4464

Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211112071016.9640-1-vinay.belgaumkar@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c

@@ -183,11 +183,15 @@ static int slpc_unset_param(struct intel_guc_slpc *slpc,
 static int slpc_force_min_freq(struct intel_guc_slpc *slpc, u32 freq)
 {
 	struct drm_i915_private *i915 = slpc_to_i915(slpc);
+	struct intel_guc *guc = slpc_to_guc(slpc);
 	intel_wakeref_t wakeref;
 	int ret = 0;
 
 	lockdep_assert_held(&slpc->lock);
 
+	if (!intel_guc_is_ready(guc))
+		return -ENODEV;
+
 	/*
 	 * This function is a little different as compared to
 	 * intel_guc_slpc_set_min_freq(). Softlimit will not be updated