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.
-Saravana
