ACPI fixes for v4.9-rc2

Specifics:
 
  - Update the ACPI WDAT-based watchdog driver to ping the hardware
    during system resume to prevent a reset from occurring after the
    resume is complete (Mika Westerberg).
 
  - Fix the return value of the pcc_mbox_request_channel() stub for
    CONFIG_PCC unset (Hoan Tran).
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Merge tag 'acpi-4.9-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull ACPI fixes from Rafael Wysocki:
 "These fix an issue related to system resume in the new WDAT-based
  watchdog driver and a return value of a stub function in the ACPI CPPC
  framework.

  Specifics:

   - Update the ACPI WDAT-based watchdog driver to ping the hardware
     during system resume to prevent a reset from occurring after the
     resume is complete (Mika Westerberg).

   - Fix the return value of the pcc_mbox_request_channel() stub for
     CONFIG_PCC unset (Hoan Tran)"

* tag 'acpi-4.9-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  watchdog: wdat_wdt: Ping the watchdog on resume
  mailbox: PCC: Fix return value of pcc_mbox_request_channel()

drivers/watchdog/wdat_wdt.c

@@ -499,6 +499,10 @@ static int wdat_wdt_resume_noirq(struct device *dev)
 		ret = wdat_wdt_enable_reboot(wdat);
 		if (ret)
 			return ret;
+
+		ret = wdat_wdt_ping(&wdat->wdd);
+		if (ret)
+			return ret;
 	}
 
 	return wdat_wdt_start(&wdat->wdd);

include/acpi/pcc.h

@@ -21,7 +21,7 @@ extern void pcc_mbox_free_channel(struct mbox_chan *chan);
 static inline struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
 							 int subspace_id)
 {
-	return NULL;
+	return ERR_PTR(-ENODEV);
 }
 static inline void pcc_mbox_free_channel(struct mbox_chan *chan) { }
 #endif