Date:   Fri,  3 Mar 2023 16:53:53 -0800
In-Reply-To: <20230304005355.746421-1-saravanak@google.com>
Message-Id: <20230304005355.746421-2-saravanak@google.com>
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References: <20230304005355.746421-1-saravanak@google.com>
Subject: [PATCH v2 1/2] driver core: Add fw_devlink.sync_state command line param
From:   Saravana Kannan <saravanak@google.com>
To:     Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Saravana Kannan <saravanak@google.com>,
        Abel Vesa <abel.vesa@linaro.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Doug Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>, kernel-team@android.com,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

When all devices that could probe have finished probing (based on
deferred_probe_timeout configuration or late_initcall() when
!CONFIG_MODULES), this parameter controls what to do with devices that
haven't yet received their sync_state() calls.

fw_devlink.sync_state=strict is the default and the driver core will
continue waiting on all consumers of a device to probe successfully
before sync_state() is called for the device. This is the default
behavior since calling sync_state() on a device when all its consumers
haven't probed could make some systems unusable/unstable. When this
option is selected, we also print the list of devices that haven't had
sync_state() called on them by the time all devices the could probe have
finished probing.

fw_devlink.sync_state=timeout will cause the driver core to give up
waiting on consumers and call sync_state() on any devices that haven't
yet received their sync_state() calls. This option is provided for
systems that won't become unusable/unstable as they might be able to
save power (depends on state of hardware before kernel starts) if all
devices get their sync_state().

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 .../admin-guide/kernel-parameters.txt         | 14 +++++
 drivers/base/base.h                           |  1 +
 drivers/base/core.c                           | 58 +++++++++++++++++++
 drivers/base/dd.c                             |  6 ++
 4 files changed, 79 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6221a1d057dd..fc5dc4dc9a5c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1582,6 +1582,20 @@
 			dependencies. This only applies for fw_devlink=on|rpm.
 			Format: <bool>
 
+	fw_devlink.sync_state =
+			[KNL] When all devices that could probe have finished
+			probing, this parameter controls what to do with
+			devices that haven't yet received their sync_state()
+			calls.
+			Format: { strict | timeout }
+			strict -- Default. Continue waiting on consumers to
+				probe successfully.
+			timeout -- Give up waiting on consumers and call
+				sync_state() on any devices that haven't yet
+				received their sync_state() calls after
+				deferred_probe_timeout has expired or by
+				late_initcall() if !CONFIG_MODULES.
+
 	gamecon.map[2|3]=
 			[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 			support via parallel port (up to 5 devices per port)
diff --git a/drivers/base/base.h b/drivers/base/base.h
index 726a12a244c0..6fcd71803d35 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -209,6 +209,7 @@ extern void device_links_no_driver(struct device *dev);
 extern bool device_links_busy(struct device *dev);
 extern void device_links_unbind_consumers(struct device *dev);
 extern void fw_devlink_drivers_done(void);
+extern void fw_devlink_probing_done(void);
 
 /* device pm support */
 void device_pm_move_to_tail(struct device *dev);
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 6878dfcbf0d6..4c7e1550bb02 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1685,6 +1685,26 @@ static int __init fw_devlink_strict_setup(char *arg)
 }
 early_param("fw_devlink.strict", fw_devlink_strict_setup);
 
+#define FW_DEVLINK_SYNC_STATE_STRICT	0
+#define FW_DEVLINK_SYNC_STATE_TIMEOUT	1
+
+static int fw_devlink_sync_state;
+static int __init fw_devlink_sync_state_setup(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (strcmp(arg, "strict") == 0) {
+		fw_devlink_sync_state = FW_DEVLINK_SYNC_STATE_STRICT;
+		return 0;
+	} else if (strcmp(arg, "timeout") == 0) {
+		fw_devlink_sync_state = FW_DEVLINK_SYNC_STATE_TIMEOUT;
+		return 0;
+	}
+	return -EINVAL;
+}
+early_param("fw_devlink.sync_state", fw_devlink_sync_state_setup);
+
 static inline u32 fw_devlink_get_flags(u8 fwlink_flags)
 {
 	if (fwlink_flags & FWLINK_FLAG_CYCLE)
@@ -1755,6 +1775,44 @@ void fw_devlink_drivers_done(void)
 	device_links_write_unlock();
 }
 
+static int fw_devlink_dev_sync_state(struct device *dev, void *data)
+{
+	struct device_link *link = to_devlink(dev);
+	struct device *sup = link->supplier;
+
+	if (!(link->flags & DL_FLAG_MANAGED) ||
+	    link->status == DL_STATE_ACTIVE || sup->state_synced ||
+	    !dev_has_sync_state(sup))
+		return 0;
+
+	if (fw_devlink_sync_state == FW_DEVLINK_SYNC_STATE_STRICT) {
+		dev_warn(sup, "sync_state() pending due to %s\n",
+			 dev_name(link->consumer));
+		return 0;
+	}
+
+	if (!list_empty(&sup->links.defer_sync))
+		return 0;
+
+	dev_warn(sup, "Timed out. Forcing sync_state()\n");
+	sup->state_synced = true;
+	get_device(sup);
+	list_add_tail(&sup->links.defer_sync, data);
+
+	return 0;
+}
+
+void fw_devlink_probing_done(void)
+{
+	LIST_HEAD(sync_list);
+
+	device_links_write_lock();
+	class_for_each_device(&devlink_class, NULL, &sync_list,
+			      fw_devlink_dev_sync_state);
+	device_links_write_unlock();
+	device_links_flush_sync_list(&sync_list, NULL);
+}
+
 /**
  * wait_for_init_devices_probe - Try to probe any device needed for init
  *
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 8def2ba08a82..84f07e0050dd 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -315,6 +315,8 @@ static void deferred_probe_timeout_work_func(struct work_struct *work)
 	list_for_each_entry(p, &deferred_probe_pending_list, deferred_probe)
 		dev_info(p->device, "deferred probe pending\n");
 	mutex_unlock(&deferred_probe_mutex);
+
+	fw_devlink_probing_done();
 }
 static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);
 
@@ -364,6 +366,10 @@ static int deferred_probe_initcall(void)
 		schedule_delayed_work(&deferred_probe_timeout_work,
 			driver_deferred_probe_timeout * HZ);
 	}
+
+	if (!IS_ENABLED(CONFIG_MODULES))
+		fw_devlink_probing_done();
+
 	return 0;
 }
 late_initcall(deferred_probe_initcall);
-- 
2.40.0.rc0.216.gc4246ad0f0-goog