On Wed, Sep 20, 2017 at 11:45:20AM +0300, sakari.ailus@xxxxxx wrote: > > >> @@ -743,11 +770,17 @@ static int at24_probe(struct i2c_client *client, const > > >> struct i2c_device_id *id) > > >> > > >> i2c_set_clientdata(client, at24); > > >> > > >> + /* enable runtime pm */ > > >> + pm_runtime_get_noresume(&client->dev); > > >> + pm_runtime_set_active(&client->dev); > > >> + pm_runtime_enable(&client->dev); > > > > Do we need this get_noresume/set_active dance? I remember it was for > > some reason needed for PCI devices, but I don't see why for I2C > > anything else than just pm_runtime_enable() would be necessary. > > You specifically do not need (all) this for PCI devices, but AFAIU for I²C > devices you do. The runtime PM status of a device is disabled by default > and the use count is zero, but on ACPI based systems the device is still > powered on. > > > > > Also, we enable runtime PM, but we don't provide any callbacks. If > > there is no callback in any level of the hierarchy, NULL would be > > returned in [3], making [2] return -ENOSYS and [1] fail. The behavior > > depends on subsystem and whether the device is attached to a > > pm_domain. In our particular case I'd guess the device would be in an > > ACPI pm_domain and that would work, but the driver is generic and must > > work in any cases. > > Agreed. I looked at the code and what actually happens here is the runtime_suspend and runtime_resume callbacks aren't set is that the first pm_runtime_put() call itself succeeds because checking the the runtime_suspend callback will be done in the work queue function. This leaves the device in RPM_ACTIVE state, which I don't think is a problem since the driver did not have explicit functions to control the device power state. Further pm_runtime_put() and pm_runtime_get() calls will succeed because the device is in RPM_ACTIVE state. So I see no reason to set the callbacks if they would not actually control regulators, clocks or GPIOs required by the device. Cc linux-pm. -- Kind regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx
