[PATCH v2 3/3] pwm: lpss: Set DPM_FLAG_SMART_SUSPEND on Cherry Trail devices

[Hans de Goede <hdegoede@redhat.com>]

As the comment above the code setting the DPM_FLAG_NO_DIRECT_COMPLETE
flag explains:

    /*
     * 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
     */

The pm-core must not skip resume to avoid the GFX0._PS0 AML code messing
with the PWM controller behind our back. But leaving the controller
runtime-suspended (skipping runtime-resume + normal-suspend) during
suspend is fine. Set the DPM_FLAG_SMART_SUSPEND flag to allow this.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v2:
- Extend comment to explain why the DPM_FLAG_SMART_SUSPEND is set
---
 drivers/pwm/pwm-lpss-platform.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-lpss-platform.c b/drivers/pwm/pwm-lpss-platform.c
index ac33861edb48..986786be1e49 100644
--- a/drivers/pwm/pwm-lpss-platform.c
+++ b/drivers/pwm/pwm-lpss-platform.c
@@ -69,9 +69,13 @@ static int pwm_lpss_probe_platform(struct platform_device *pdev)
 	 *    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
+	 *
+	 * Leaving the controller runtime-suspended (skipping runtime-resume +
+	 * normal-suspend) during suspend is fine.
 	 */
 	if (info->other_devices_aml_touches_pwm_regs)
-		dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_NO_DIRECT_COMPLETE);
+		dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_NO_DIRECT_COMPLETE|
+						    DPM_FLAG_SMART_SUSPEND);
 
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
-- 
2.28.0