If a parent device is also a supplier to a child device, fw_devlink=on (correctly) delays the probe() of the child device until the probe() of the parent finishes successfully. However, some drivers of such parent devices (where parent is also a supplier) incorrectly expect the child device to finish probing successfully as soon as they are added using device_add() and before the probe() of the parent device has completed successfully. While this might have worked before, this is not guaranteed by driver core. fw_devlink=on catches/breaks such drivers. One example of such a case is discussed in the link mentioned below. Add a flag to make fw_devlink=on not enforce these supplier-consumer relationships, so these drivers can continue working. The flag is intentionally called BROKEN_PARENT so it's clear that this flag shouldn't be used in the normal case and that there's a problem with the driver. Link: https://lore.kernel.org/netdev/CAGETcx_uj0V4DChME-gy5HGKTYnxLBX=TH2rag29f_p=UcG+Tg@xxxxxxxxxxxxxx/ Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx> --- drivers/base/core.c | 22 ++++++++++++++++++++++ include/linux/fwnode.h | 3 +++ 2 files changed, 25 insertions(+) diff --git a/drivers/base/core.c b/drivers/base/core.c index f6360490a4a3..2cc34f8ff051 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -1719,6 +1719,28 @@ static int fw_devlink_create_devlink(struct device *con, struct device *sup_dev; int ret = 0; + /* + * In some cases, a device P might also be a supplier to its child node + * C. However, this would defer the probe of C until the probe of P + * completes successfully. This is perfectly fine in the device driver + * model. device_add() doesn't guarantee probe completion of the device + * by the time it returns. + * + * However, there are a few drivers that assume C will finish probing + * as soon as it's added and before P finishes probing. While this is a + * broken assumption that needs the driver to be fixed, we don't want + * to block fw_devlink improvements because of these drivers. + * + * So, we provide a flag to let fw_devlink know not to delay the probe + * of C until the probe of P completes successfully. + * + * When such a flag is set, we can't create device links with P as the + * supplier of C as that would delay the probe of C. + */ + if (sup_handle->flags & FWNODE_FLAG_BROKEN_PARENT && + fwnode_is_ancestor_of(sup_handle, con->fwnode)) + return -EINVAL; + sup_dev = get_dev_from_fwnode(sup_handle); if (sup_dev) { /* diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h index 59828516ebaf..9382065e6ff8 100644 --- a/include/linux/fwnode.h +++ b/include/linux/fwnode.h @@ -22,10 +22,13 @@ struct device; * LINKS_ADDED: The fwnode has already be parsed to add fwnode links. * NOT_DEVICE: The fwnode will never be populated as a struct device. * INITIALIZED: The hardware corresponding to fwnode has been initialized. + * BROKEN_PARENT: The driver of this fwnode/device expects the child devices to + * probe as soon as they are added. */ #define FWNODE_FLAG_LINKS_ADDED BIT(0) #define FWNODE_FLAG_NOT_DEVICE BIT(1) #define FWNODE_FLAG_INITIALIZED BIT(2) +#define FWNODE_FLAG_BROKEN_PARENT BIT(3) struct fwnode_handle { struct fwnode_handle *secondary; -- 2.33.0.rc2.250.ged5fa647cd-goog
