driver core: Add wait_for_init_devices_probe helper function

Some devices might need to be probed and bound successfully before the
kernel boot sequence can finish and move on to init/userspace. For
example, a network interface might need to be bound to be able to mount
a NFS rootfs.

With fw_devlink=on by default, some of these devices might be blocked
from probing because they are waiting on a optional supplier that
doesn't have a driver. While fw_devlink will eventually identify such
devices and unblock the probing automatically, it might be too late by
the time it unblocks the probing of devices. For example, the IP4
autoconfig might timeout before fw_devlink unblocks probing of the
network interface.

This function is available to temporarily try and probe all devices that
have a driver even if some of their suppliers haven't been added or
don't have drivers.

The drivers can then decide which of the suppliers are optional vs
mandatory and probe the device if possible. By the time this function
returns, all such "best effort" probes are guaranteed to be completed.
If a device successfully probes in this mode, we delete all fw_devlink
discovered dependencies of that device where the supplier hasn't yet
probed successfully because they have to be optional dependencies.

This also means that some devices that aren't needed for init and could
have waited for their optional supplier to probe (when the supplier's
module is loaded later on) would end up probing prematurely with limited
functionality.  So call this function only when boot would fail without
it.

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20220601070707.3946847-5-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 11b0fb6414d3..4a55fbb7e0da 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -172,7 +172,7 @@ static bool driver_deferred_probe_enable;
  * changes in the midst of a probe, then deferred processing should be triggered
  * again.
  */
-static void driver_deferred_probe_trigger(void)
+void driver_deferred_probe_trigger(void)
 {
 	if (!driver_deferred_probe_enable)
 		return;
@@ -580,7 +580,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 {
 	bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) &&
 			   !drv->suppress_bind_attrs;
-	int ret;
+	int ret, link_ret;
 
 	if (defer_all_probes) {
 		/*
@@ -592,9 +592,9 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 		return -EPROBE_DEFER;
 	}
 
-	ret = device_links_check_suppliers(dev);
-	if (ret)
-		return ret;
+	link_ret = device_links_check_suppliers(dev);
+	if (link_ret == -EPROBE_DEFER)
+		return link_ret;
 
 	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
 		 drv->bus->name, __func__, drv->name, dev_name(dev));
@@ -634,6 +634,15 @@ re_probe:
 	ret = call_driver_probe(dev, drv);
 	if (ret) {
 		/*
+		 * If fw_devlink_best_effort is active (denoted by -EAGAIN), the
+		 * device might actually probe properly once some of its missing
+		 * suppliers have probed. So, treat this as if the driver
+		 * returned -EPROBE_DEFER.
+		 */
+		if (link_ret == -EAGAIN)
+			ret = -EPROBE_DEFER;
+
+		/*
 		 * Return probe errors as positive values so that the callers
 		 * can distinguish them from other errors.
 		 */