pwm: lpss: Use DPM_FLAG_NO_DIRECT_COMPLETE instead of declaring a prepare handler

ACPI LPSS devices use direct-complete style suspend/resume handling by
default. We set the DPM_FLAG_SMART_PREPARE and define a prepare handler
to disable this on Cherry Trail devices.

Clean this up a bit by setting the DPM_FLAG_NO_DIRECT_COMPLETE flag for
Cherry Trail devices, instead of defining a prepare handler.

While at it also improve the comment explaining why this is necessary.
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-lpss-platform.c

@@ -58,7 +58,21 @@ static int pwm_lpss_probe_platform(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, lpwm);
 
-	dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_SMART_PREPARE);
+	/*
+	 * On Cherry Trail devices the GFX0._PS0 AML checks if the controller
+	 * is on and if it is not on it turns it on and restores what it
+	 * believes is the correct state to the PWM controller.
+	 * Because of this we must disallow direct-complete, which keeps the
+	 * controller (runtime)suspended on resume, to avoid 2 issues:
+	 * 1. The controller getting turned on without the linux-pm code
+	 *    knowing about this. On devices where the controller is unused
+	 *    this causes it to stay on during the next suspend causing high
+	 *    battery drain (because S0i3 is not reached)
+	 * 2. The state restoring code unexpectedly messing with the controller
+	 */
+	if (info->other_devices_aml_touches_pwm_regs)
+		dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_NO_DIRECT_COMPLETE);
+
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 
@@ -73,24 +87,6 @@ static int pwm_lpss_remove_platform(struct platform_device *pdev)
 	return pwm_lpss_remove(lpwm);
 }
 
-static int pwm_lpss_prepare(struct device *dev)
-{
-	struct pwm_lpss_chip *lpwm = dev_get_drvdata(dev);
-
-	/*
-	 * If other device's AML code touches the PWM regs on suspend/resume
-	 * force runtime-resume the PWM controller to allow this.
-	 */
-	if (lpwm->info->other_devices_aml_touches_pwm_regs)
-		return 0; /* Force runtime-resume */
-
-	return 1; /* If runtime-suspended leave as is */
-}
-
-static const struct dev_pm_ops pwm_lpss_platform_pm_ops = {
-	.prepare = pwm_lpss_prepare,
-};
-
 static const struct acpi_device_id pwm_lpss_acpi_match[] = {
 	{ "80860F09", (unsigned long)&pwm_lpss_byt_info },
 	{ "80862288", (unsigned long)&pwm_lpss_bsw_info },
@@ -104,7 +100,6 @@ static struct platform_driver pwm_lpss_driver_platform = {
 	.driver = {
 		.name = "pwm-lpss",
 		.acpi_match_table = pwm_lpss_acpi_match,
-		.pm = &pwm_lpss_platform_pm_ops,
 	},
 	.probe = pwm_lpss_probe_platform,
 	.remove = pwm_lpss_remove_platform,