intel_ips -- ensure we do not enable gpu turbo mode without driver linkage

Both when polling the current turbo status (in poll_turbo_status mode)
and when handling thermal events (in ips_irq_handler) the current status
of GPU turbo is updated to match the hardware status.  However if during
driver initialisation we were unable aquire linkage to the i915 driver
enabling GPU turbo will lead to an oops on the first attempt to determine
GPU busy status.

Ensure that we do not enable GPU turbo unless we have driver linkage.

BugLink: http://bugs.launchpad.net/bugs/632430
Cc: stable@kernel.org
Signed-off-by: NAndy Whitcroft <apw@canonical.com>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>

drivers/platform/x86/intel_ips.c

@@ -715,7 +715,8 @@ static void update_turbo_limits(struct ips_driver *ips)
 	u32 hts = thm_readl(THM_HTS);
 
 	ips->cpu_turbo_enabled = !(hts & HTS_PCTD_DIS);
-	ips->gpu_turbo_enabled = !(hts & HTS_GTD_DIS);
+	if (ips->gpu_busy)
+		ips->gpu_turbo_enabled = !(hts & HTS_GTD_DIS);
 	ips->core_power_limit = thm_readw(THM_MPCPC);
 	ips->mch_power_limit = thm_readw(THM_MMGPC);
 	ips->mcp_temp_limit = thm_readw(THM_PTL);
@@ -1185,7 +1186,8 @@ static irqreturn_t ips_irq_handler(int irq, void *arg)
 				STS_GPL_SHIFT;
 			/* ignore EC CPU vs GPU pref */
 			ips->cpu_turbo_enabled = !(sts & STS_PCTD_DIS);
-			ips->gpu_turbo_enabled = !(sts & STS_GTD_DIS);
+			if (ips->gpu_busy)
+				ips->gpu_turbo_enabled = !(sts & STS_GTD_DIS);
 			ips->mcp_temp_limit = (sts & STS_PTL_MASK) >>
 				STS_PTL_SHIFT;
 			ips->mcp_power_limit = (tc1 & STS_PPL_MASK) >>