On Tue, Aug 31, 2021 at 9:59 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
>
> On Tue, Aug 31, 2021 at 6:56 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> >
> > Hi Saravana, Rafael, Stephen,
> >
> > I have observed an issue with a driver's ->sync_state() callback that
> > doesn't get called, even if consumers/supplier device links conditions
> > should have been satisfied. I have narrowed down the problem, but I am
> > not sure what is the best solution to fix it, hence I am turning to
> > you for some discussion/advice.
> >
> > I have two test platform drivers, one that matches on the
> > "test,pm-domains-test" compatible string (this driver also has the
> > ->sync_state() callback assigned) and another driver that matches on
> > "test,runtime-pm-test".
> >
> > This is the relevant part in my DTS file:
> >
> > pm_domain_test {
> > compatible = "test,pm-domains-test";
> >
> > pdParent: power-domain-parent {
> > #power-domain-cells = <0>;
> > };
> >
> > pdChild: power-domain-child {
> > #power-domain-cells = <0>;
> > power-domains = <&pdParent>;
> > };
> > };
> >
> > soctest: soctest {
> > compatible = "simple-bus";
> >
> > rpmtest0 {
> > compatible = "test,runtime-pm-test";
> > power-domains = <&pdParent>;
> > };
> > };
> >
> > During boot the fw_devlinks are being created and their corresponding
> > links. With some debug enabled this shows some of the interesting
> > parts that are being printed to the log:
> >
> > [ 0.041539] device: 'pm_domain_test': device_add
> > [ 0.041629] OF: Not linking pm_domain_test to pm_domain_test - is descendant
> > [ 0.041718] device: 'soctest': device_add
> > [ 0.041803] OF: Linking rpmtest0 (consumer) to pm_domain_test (supplier)
> > [ 0.041829] device: 'platform:pm_domain_test--platform:soctest': device_add
> > [ 0.041892] platform soctest: Linked as a sync state only consumer
> > to pm_domain_test
> > [ 0.041957] OF: create child: /soctest/rpmtest0
> > [ 0.041995] device: 'soctest:rpmtest0': device_add
> > [ 0.042072] device:
> > 'platform:pm_domain_test--platform:soctest:rpmtest0': device_add
> > [ 0.042132] devices_kset: Moving soctest:rpmtest0 to end of list
> > [ 0.042141] platform soctest:rpmtest0: Linked as a consumer to pm_domain_test
> >
> > The interesting thing here is the "sync state only" link that gets
> > created. I assume there are good reasons for creating this link, even
> > if I fail to understand exactly why.
>
> In general there's a good reason for creating these links from parent
> devices of the consumer to the supplier. It is documented in the code
> under __fw_devlink_link_to_consumers().
>
> /*
> * If consumer device is not available yet, make a "proxy"
> * SYNC_STATE_ONLY link from the consumer's parent device to
> * the supplier device. This is necessary to make sure the
> * supplier doesn't get a sync_state() callback before the real
> * consumer can create a device link to the supplier.
> *
> * This proxy link step is needed to handle the case where the
> * consumer's parent device is added before the supplier.
> */
>
> and under __fw_devlink_link_to_suppliers().
>
> /*
> * Make "proxy" SYNC_STATE_ONLY device links to represent the needs of
> * all the descendants. This proxy link step is needed to handle the
> * case where the supplier is added before the consumer's parent device
> * (@dev).
> */
>
>
> >
> > In any case, the sync state only link never gets dropped, which I
> > assume is because there is no driver getting bound for the "soctest"
> > device (it has only the "simple-bus" compatible).
>
> Yeah, you've identified the problem correctly. I've been thinking
> about this possibility (and all the side effects a fix might have). I
> can send out a fix for this soon (within a week or so).
>
> > In other words, it doesn't matter that both the rpmtest0 and the
> > pm_domain_test devices are probed, thus satisfying the
> > supplier/consumer conditions, the ->sync_state() callback doesn't get
> > called anyway.
> >
> > Can you perhaps help to point me in a direction of how to best fix this problem?
>
> I hope you are okay with me sending a fix.
Ulf,
Could you give this a shot please?
https://lore.kernel.org/lkml/20210831224510.703253-1-saravanak@xxxxxxxxxx/T/#u
-Saravana
