mfd / platform: cros_ec_debugfs: Expose resume result via debugfs

For ECs that support it, the EC returns the number of slp_s0
transitions and whether or not there was a timeout in the resume
response. Expose the last resume result to usermode via debugfs so
that usermode can detect and report S0ix timeouts.
Signed-off-by: Evan Green <evgreen@chromium.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Documentation/ABI/testing/debugfs-cros-ec

@@ -32,3 +32,25 @@ Description:
 		is used for synchronizing the AP host time with the EC
 		log. An error is returned if the command is not supported
 		by the EC or there is a communication problem.
+
+What:		/sys/kernel/debug/<cros-ec-device>/last_resume_result
+Date:		June 2019
+KernelVersion:	5.3
+Description:
+		Some ECs have a feature where they will track transitions to
+		the (Intel) processor's SLP_S0 line, in order to detect cases
+		where a system failed to go into S0ix. When the system resumes,
+		an EC with this feature will return a summary of SLP_S0
+		transitions that occurred. The last_resume_result file returns
+		the most recent response from the AP's resume message to the EC.
+
+		The bottom 31 bits contain a count of the number of SLP_S0
+		transitions that occurred since the suspend message was
+		received. Bit 31 is set if the EC attempted to wake the
+		system due to a timeout when watching for SLP_S0 transitions.
+		Callers can use this to detect a wake from the EC due to
+		S0ix timeouts. The result will be zero if no suspend
+		transitions have been attempted, or the EC does not support
+		this feature.
+
+		Output will be in the format: "0x%08x\n".

drivers/mfd/cros_ec.c

@@ -110,12 +110,16 @@ static int cros_ec_sleep_event(struct cros_ec_device *ec_dev, u8 sleep_event)
 
 	/* For now, report failure to transition to S0ix with a warning. */
 	if (ret >= 0 && ec_dev->host_sleep_v1 &&
-	    (sleep_event == HOST_SLEEP_EVENT_S0IX_RESUME))
+	    (sleep_event == HOST_SLEEP_EVENT_S0IX_RESUME)) {
+		ec_dev->last_resume_result =
+			buf.u.resp1.resume_response.sleep_transitions;
+
 		WARN_ONCE(buf.u.resp1.resume_response.sleep_transitions &
 			  EC_HOST_RESUME_SLEEP_TIMEOUT,
 			  "EC detected sleep transition timeout. Total slp_s0 transitions: %d",
 			  buf.u.resp1.resume_response.sleep_transitions &
 			  EC_HOST_RESUME_SLEEP_TRANSITIONS_MASK);
+	}
 
 	return ret;
 }

drivers/platform/chrome/cros_ec_debugfs.c

@@ -447,6 +447,9 @@ static int cros_ec_debugfs_probe(struct platform_device *pd)
 	debugfs_create_file("uptime", 0444, debug_info->dir, debug_info,
 			    &cros_ec_uptime_fops);
 
+	debugfs_create_x32("last_resume_result", 0444, debug_info->dir,
+			   &ec->ec_dev->last_resume_result);
+
 	ec->debug_info = debug_info;
 
 	dev_set_drvdata(&pd->dev, ec);

include/linux/mfd/cros_ec.h

@@ -163,6 +163,7 @@ struct cros_ec_device {
 	struct ec_response_get_next_event_v1 event_data;
 	int event_size;
 	u32 host_event_wake_mask;
+	u32 last_resume_result;
 };
 
 /**