PM regression with commit 5de85b9d57ab PM runtime re-init in v4.5-rc1

Hi,

* Ulf Hansson [off-list ref] [160202 02:43]:

For the omap_hsmmc and likely also other omap drivers, which needs more
than one attempt to ->probe() (returning -EPROBE_DEFER), this commit
causes a regression at the PM domain level (omap hwmod).

The reason is that the drivers don't put back the device into low power
state while bailing out in ->probe to return -EPROBE_DEFER. This leads to
that pm_runtime_reinit() in driver core, is re-initializing the runtime PM
status from RPM_ACTIVE to RPM_SUSPENDED.

Yup, that's the bug here. It seems that we never call the runtime_suspend
callback at the end of a first failed device driver probe if the driver
has set pm_runtime_use_autosuspend. Only rpm_idle runtime_idle callback
gets called. So the device stays on.

This does not happen if pm_runtime_dont_use_autosuspend() is added to
the end of the device driver probe before pm_runtime_put_sync().

The next ->probe() attempt then triggers the ->runtime_resume() callback
to be invoked, which means this happens two times in a row. At the PM
domain level (omap hwmod) this is being treated as an error and thus the
runtime PM status of the device isn't correctly synchronized with the
runtime PM core.

That's a valid error though, let's not remove it. The reason why we
call runtime_resume() twice is because runtime_suspend callback never
gets called like I explain above.

In the end, ->probe() anyway succeeds (as the driver don't checks the
error code from the runtime PM APIs), but results in that the PM domain
always stays powered on. This because of the runtime PM core believes the
device is RPM_SUSPENDED.

FYI, the following allows runtime_suspend callback to get called at the
end of a failed driver probe so the hardware state matches the PM runtime
state. Need to debug more.

Regards,

Tony

8< ------------

--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c

@@ -2232,6 +2232,7 @@ err_irq:
 		dma_release_channel(host->tx_chan);
 	if (host->rx_chan)
 		dma_release_channel(host->rx_chan);
+	pm_runtime_dont_use_autosuspend(host->dev);
 	pm_runtime_put_sync(host->dev);
 	pm_runtime_disable(host->dev);
 	if (host->dbclk)