On Tue, Apr 12, 2016 at 09:57:35AM +0200, Linus Walleij wrote: > When using a certain I2C device with runtime PM enabled on > a certain I2C bus adaper the following happens: > > struct amba_device *foo > \ > struct i2c_adapter *bar > \ > struct i2c_client *baz > > The AMBA device foo has its device PM struct set to ignore > children with pm_suspend_ignore_children(&foo->dev, true). > This makes runtime PM work just fine locally in the driver: > the fact that devices on the bus are suspended or resumed > individually does not affect its operation, and the hardware > does not power up unless transferring messages. > > However this child ignorance property is not inherited into > the struct i2c_adapter *bar. > > On system suspend things will work fine. > > On system resume the following annoying phenomenon occurs: > > - In the pm_runtime_force_resume() path of > struct i2c_client *baz, pm_runtime_set_active(&baz->dev); is > eventually called. > > - This becomes __pm_runtime_set_status(&baz->dev, RPM_ACTIVE); > > - __pm_runtime_set_status() detects that RPM state is changed, > and checks whether the parent is: > not active (RPM_ACTIVE) and not ignoring its children > If this happens it concludes something is wrong, because > a parent that is not ignoring its children must be active > before any children activate. > > - Since the struct i2c_adapter *bar does not ignore > its children, the PM core thinks that it must indeed go > online before its children, the check bails out with > -EBUSY, i.e. the i2c_client *baz thinks it can't work > because it's parent is not online, and it respects its > parent. > > - In the driver the .resume() callback returns -EBUSY from > the runtime_force_resume() call as per above. This leaves > the device in a suspended state, leading to bad behaviour > later when the device is used. The following debug > print is made with an extra printg patch but illustrates > the problem: > > [ 17.040832] bh1780 2-0029: parent (i2c-2) is not active > parent->power.ignore_children = 0 > [ 17.040832] bh1780 2-0029: pm_runtime_force_resume: > pm_runtime_set_active() failed (-16) > [ 17.040863] dpm_run_callback(): > pm_runtime_force_resume+0x0/0x88 returns -16 > [ 17.040863] PM: Device 2-0029 failed to resume: error -16 > > Fix this by letting all struct i2c_adapter:s ignore their > children: i2c children have no business doing keeping > their parents awake: they are completely autonomous > devices that just use their parent to talk, a usecase > which must be power managed in the host on a per-message > basis. > > Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx> > Cc: Mark Brown <broonie@xxxxxxxxxx> > Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> > Cc: linux-pm@xxxxxxxxxxxxxxx > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> Applied to for-next, thanks!
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