On Wed, Sep 15, 2021 at 7:09 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > When we have a dependency of the form: > > Device-A -> Device-C > Device-B > > Device-C -> Device-B > > Where, > * Indentation denotes "child of" parent in previous line. > * X -> Y denotes X is consumer of Y based on firmware (Eg: DT). > > We have cyclic dependency: device-A -> device-C -> device-B -> device-A > > fw_devlink current treats device-C -> device-B dependency as an invalid > dependency and doesn't enforce it but leaves the rest of the > dependencies as is. > > While the current behavior is necessary, it is not sufficient if the > false dependency in this example is actually device-A -> device-C. When > this is the case, device-C will correctly probe defer waiting for > device-B to be added, but device-A will be incorrectly probe deferred by > fw_devlink waiting on device-C to probe successfully. Due to this, none > of the devices in the cycle will end up probing. > > To fix this, we need to go relax all the dependencies in the cycle like > we already do in the other instances where fw_devlink detects cycles. > A real world example of this was reported[1] and analyzed[2]. > > [1] - https://lore.kernel.org/lkml/0a2c4106-7f48-2bb5-048e-8c001a7c3fda@xxxxxxxxxxx/ > [2] - https://lore.kernel.org/lkml/CAGETcx8peaew90SWiux=TyvuGgvTQOmO4BFALz7aj0Za5QdNFQ@xxxxxxxxxxxxxx/ > Fixes: f9aa460672c9 ("driver core: Refactor fw_devlink feature") > Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx> > Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > --- > drivers/base/core.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index e65dd803a453..316df6027093 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1772,14 +1772,21 @@ static int fw_devlink_create_devlink(struct device *con, > * be broken by applying logic. Check for these types of cycles and > * break them so that devices in the cycle probe properly. > * > - * If the supplier's parent is dependent on the consumer, then > - * the consumer-supplier dependency is a false dependency. So, > - * treat it as an invalid link. > + * If the supplier's parent is dependent on the consumer, then the > + * consumer and supplier have a cyclic dependency. Since fw_devlink > + * can't tell which of the inferred dependencies are incorrect, don't > + * enforce probe ordering between any of the devices in this cyclic > + * dependency. Do this by relaxing all the fw_devlink device links in > + * this cycle and by treating the fwnode link between the consumer and > + * the supplier as an invalid dependency. > */ > sup_dev = fwnode_get_next_parent_dev(sup_handle); > if (sup_dev && device_is_dependent(con, sup_dev)) { > - dev_dbg(con, "Not linking to %pfwP - False link\n", > - sup_handle); > + dev_info(con, "Fixing up cyclic dependency with %pfwP (%s)\n", > + sup_handle, dev_name(sup_dev)); Why not dev_dbg()? Other than this, the change makes sense to me. > + device_links_write_lock(); > + fw_devlink_relax_cycle(con, sup_dev); > + device_links_write_unlock(); > ret = -EINVAL; > } else { > /* > -- > 2.33.0.309.g3052b89438-goog >
