sleep/resume: Set fan control to auto before sleep

On some systems, like the X1 Carbon Gen 12 and T14s Gen 5, unless the
fan is set to auto before suspension it continues running at the set fan
speed during suspend. See #36.

Introduce a mechanism to disable zcfan's fan setting and set the fan
level to auto when sleep is imminent, and reenable it when we have
resumed. systemd users can do this transparently using the supplied
service files, others can manually signal with SIGPWR and SIGUSR2 at
their convenience.

Author: cdown

Makefile

@@ -48,6 +48,8 @@ install: all
 	mkdir -p $(DESTDIR)$(bindir)/
 	$(INSTALL) -pt $(DESTDIR)$(bindir)/ $(EXECUTABLES)
 	$(INSTALL) -Dp -m 644 $(SERVICE) $(DESTDIR)$(prefix)/lib/systemd/system/$(SERVICE)
+	$(INSTALL) -Dp -m 644 zcfan-sleep.service $(DESTDIR)$(prefix)/lib/systemd/system/zcfan-sleep.service
+	$(INSTALL) -Dp -m 644 zcfan-resume.service $(DESTDIR)$(prefix)/lib/systemd/system/zcfan-resume.service
 	$(INSTALL) -Dp -m 644 zcfan.1 $(DESTDIR)$(mandir)/man1/zcfan.1
 
 lint:

README.md

@@ -69,6 +69,10 @@ Run `make`.
     - At runtime: `rmmod thinkpad_acpi && modprobe thinkpad_acpi fan_control=1`
     - By default: `echo options thinkpad_acpi fan_control=1 > /etc/modprobe.d/99-fancontrol.conf`
 3. Run `zcfan` as root (or use the `zcfan` systemd service provided)
+4. If you run a laptop which keeps the fan running during suspend, you will also
+   want to send `SIGPWR` before sleep and `SIGUSR2` before wakeup to avoid
+   that. For systemd users, enable the `zcfan-sleep.service` and
+   `zcfan-resume.service` units to do that automatically.
 
 ## Disclaimer
 

zcfan-resume.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Reload zcfan after waking up from suspend
+After=sysinit.target
+After=suspend.target
+After=suspend-then-hibernate.target
+After=hybrid-sleep.target
+After=hibernate.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/pkill -x -USR2 zcfan
+
+[Install]
+WantedBy=sleep.target

zcfan-sleep.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Notify zcfan of imminent sleep
+Before=sleep.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/pkill -x -PWR zcfan
+# Executing the signal handler races with sleep, so delay a bit
+ExecStart=sleep 1
+
+[Install]
+WantedBy=sleep.target

zcfan.c

@@ -58,6 +58,8 @@ static const unsigned int tick_hysteresis = 3;
 static char output_buf[512];
 static const struct Rule *current_rule = NULL;
 static volatile sig_atomic_t run = 1;
+static volatile sig_atomic_t pending_sleep = 0;
+static volatile sig_atomic_t pending_resume = 0;
 static int first_tick = 1; /* Stop running if errors are immediate */
 static glob_t temp_files;
 
@@ -345,6 +347,16 @@ static void stop(int sig) {
     run = 0;
 }
 
+static void handle_sigpwr(int sig) {
+    (void)sig;
+    pending_sleep = 1;
+}
+
+static void handle_sigusr2(int sig) {
+    (void)sig;
+    pending_resume = 1;
+}
+
 int main(int argc, char *argv[]) {
     const struct sigaction sa_exit = {
         .sa_handler = stop,
@@ -363,6 +375,15 @@ int main(int argc, char *argv[]) {
     print_thresholds();
     expect(sigaction(SIGTERM, &sa_exit, NULL) == 0);
     expect(sigaction(SIGINT, &sa_exit, NULL) == 0);
+    expect(
+        sigaction(SIGPWR,
+                  &(const struct sigaction){.sa_handler = handle_sigpwr},
+                  NULL) == 0);
+    expect(
+        sigaction(SIGUSR2,
+                  &(const struct sigaction){.sa_handler = handle_sigusr2},
+                  NULL) == 0);
+
     expect(setvbuf(stdout, output_buf, _IOLBF, sizeof(output_buf)) == 0);
 
     if (!full_speed_supported()) {
@@ -374,16 +395,35 @@ int main(int argc, char *argv[]) {
     write_watchdog_timeout(watchdog_secs);
     populate_temp_files();
 
+    int fan_control_enabled = 1;
+
     while (run) {
-        enum set_fan_status set = set_fan_level();
-        if (set != FAN_LEVEL_SET) {
-            maybe_ping_watchdog();
+        if (fan_control_enabled) {
+            enum set_fan_status set = set_fan_level();
+            if (set != FAN_LEVEL_SET) {
+                maybe_ping_watchdog();
+            }
         }
-
         if (run) {
             sleep(1);
             first_tick = 0;
         }
+        if (pending_sleep) {
+            pending_sleep = 0;
+            info("Fan control disabled for sleep\n");
+            if (write_fan_level("auto") == 0)
+                write_watchdog_timeout(0);
+            fan_control_enabled = 0;
+        }
+        if (pending_resume) {
+            pending_resume = 0;
+            info("Fan control enabled for resume\n");
+            fan_control_enabled = 1;
+            expect(current_rule);
+            write_fan_level(current_rule->tpacpi_level);
+            write_watchdog_timeout(watchdog_secs);
+        }
+
     }
 
     globfree(&temp_files);