wifi: iwlwifi: fix the check for the SCRATCH register upon resume

We can't rely on the SCRATCH register being 0 on platform that power
gate the NIC in S3. Even in those platforms, the SCRATCH register is
still returning 0x1010000.

Make sure that we understand that those platforms have powered off the
device.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219597
Fixes: cb347bd ("wifi: iwlwifi: mvm: fix hibernation")
Signed-off-by: Emmanuel Grumbach <[email protected]>
Signed-off-by: Miri Korenblit <[email protected]>
Link: https://patch.msgid.link/20250420095642.a7e082ee785c.I9418d76f860f54261cfa89e1f7ac10300904ba40@changeid
Signed-off-by: Johannes Berg <[email protected]>

Author: egrumbach

drivers/net/wireless/intel/iwlwifi/iwl-csr.h

@@ -148,6 +148,7 @@
  * during a error FW error.
  */
 #define CSR_FUNC_SCRATCH_INIT_VALUE		(0x01010101)
+#define CSR_FUNC_SCRATCH_POWER_OFF_MASK		0xFFFF
 
 /* Bits for CSR_HW_IF_CONFIG_REG */
 #define CSR_HW_IF_CONFIG_REG_MSK_MAC_STEP_DASH	(0x0000000F)

drivers/net/wireless/intel/iwlwifi/pcie/drv.c

@@ -1736,11 +1736,13 @@ static int _iwl_pci_resume(struct device *device, bool restore)
 	 * Scratch value was altered, this means the device was powered off, we
 	 * need to reset it completely.
 	 * Note: MAC (bits 0:7) will be cleared upon suspend even with wowlan,
-	 * so assume that any bits there mean that the device is usable.
+	 * but not bits [15:8]. So if we have bits set in lower word, assume
+	 * the device is alive.
 	 * For older devices, just try silently to grab the NIC.
 	 */
 	if (trans->trans_cfg->device_family >= IWL_DEVICE_FAMILY_BZ) {
-		if (!iwl_read32(trans, CSR_FUNC_SCRATCH))
+		if (!(iwl_read32(trans, CSR_FUNC_SCRATCH) &
+		      CSR_FUNC_SCRATCH_POWER_OFF_MASK))
 			device_was_powered_off = true;
 	} else {
 		/*