Alan,
> > When we also are I2C slave, we need to disable runtime PM because the
> > address detection mechanism needs to be active all the time. However, we
> > can reenable runtime PM once the slave instance was unregistered. So,
> > use pm_runtime_disable/enable to achieve this, since it has proper
> > refcounting. pm_runtime_allow/forbid is like a global switch which is
> > unsuitable here.
> >
> > Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >
> > I'd be grateful to get an ACK from a runtime PM expert to verify that my
> > assumptions match reality :)
>
> Yes, disabling runtime PM will do what you want. However you might
> consider using pm_runtime_get_sync() and pm_runtime_put() instead,
> because pm_runtime_enable() does not check to see if the device is idle
> and can be suspended right away. Alternatively, you can call
> pm_runtime_idle() after pm_runtime_enable().
Thank you for your answer! I think I'll go for the get/put solution
here.
I have another case, may I ask your advice about this, too? When an I2C
bus is marked in DT as multi-master, then RuntimePM also needs to be
disabled, because arbitration detection needs to stay awake. I am
currently implementing this for the i2c-rcar driver:
- pm_runtime_enable(dev);
+ /* No RuntimePM in multi-master to keep arbitration working */
+ if (!of_get_property(dev->of_node, "multi-master", NULL)) {
+ pm_runtime_enable(dev);
+ priv->flags |= ID_P_PM;
+ }
+
pm_runtime_get_sync(dev);
...
@@ -664,7 +673,8 @@ static int rcar_i2c_remove(struct platform_device *pdev)
struct device *dev = &pdev->dev;
i2c_del_adapter(&priv->adap);
- pm_runtime_disable(dev);
+ if (priv->flags & ID_P_PM)
+ pm_runtime_disable(dev);
return 0;
}
Here, I'd tend to keep using enable/disable, although get/put would
probably also work. What is the rule of thumb using this pattern or the
other?
> pm_runtime_allow/forbid is even more unsuitable than you said, because
> it can be overridden by the user.
Yeah, I realized his today, too.
Thanks!
Wolfram
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