Date:   Mon,  6 Feb 2023 17:41:58 -0800
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References: <20230207014207.1678715-1-saravanak@google.com>
Subject: [PATCH v3 06/12] driver core: fw_devlink: Allow marking a fwnode link
 as being part of a cycle
From:   Saravana Kannan <saravanak@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Cristian Marussi <cristian.marussi@arm.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>, Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Magnus Damm <magnus.damm@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Daniel Scally <djrscally@gmail.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Len Brown <lenb@kernel.org>,
        Saravana Kannan <saravanak@google.com>,
        "=?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?=" <rafal@milecki.pl>
Cc:     Abel Vesa <abel.vesa@linaro.org>,
        Alexander Stein <alexander.stein@ew.tq-group.com>,
        Tony Lindgren <tony@atomide.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        John Stultz <jstultz@google.com>,
        Doug Anderson <dianders@chromium.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Maxim Kiselev <bigunclemax@gmail.com>,
        Maxim Kochetkov <fido_max@inbox.ru>,
        Luca Weiss <luca.weiss@fairphone.com>,
        Colin Foster <colin.foster@in-advantage.com>,
        Martin Kepplinger <martin.kepplinger@puri.sm>,
        Jean-Philippe Brucker <jpb@kernel.org>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        kernel-team@android.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-gpio@vger.kernel.org,
        linux-mtd@lists.infradead.org, devicetree@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org, linux-acpi@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

To improve detection and handling of dependency cycles, we need to be
able to mark fwnode links as being part of cycles. fwnode links marked
as being part of a cycle should not block their consumers from probing.

Fixes: 2de9d8e0d2fe ("driver core: fw_devlink: Improve handling of cyclic dependencies")
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Colin Foster <colin.foster@in-advantage.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
---
 drivers/base/core.c    | 50 +++++++++++++++++++++++++++++++++---------
 include/linux/fwnode.h | 11 +++++++++-
 2 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 071c454844d6..4869b6fdfeaf 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -76,13 +76,15 @@ static bool fw_devlink_best_effort;
  * are ignored and there is no reference counting.
  */
 static int __fwnode_link_add(struct fwnode_handle *con,
-			     struct fwnode_handle *sup)
+			     struct fwnode_handle *sup, u8 flags)
 {
 	struct fwnode_link *link;
 
 	list_for_each_entry(link, &sup->consumers, s_hook)
-		if (link->consumer == con)
+		if (link->consumer == con) {
+			link->flags |= flags;
 			return 0;
+		}
 
 	link = kzalloc(sizeof(*link), GFP_KERNEL);
 	if (!link)
@@ -92,6 +94,7 @@ static int __fwnode_link_add(struct fwnode_handle *con,
 	INIT_LIST_HEAD(&link->s_hook);
 	link->consumer = con;
 	INIT_LIST_HEAD(&link->c_hook);
+	link->flags = flags;
 
 	list_add(&link->s_hook, &sup->consumers);
 	list_add(&link->c_hook, &con->suppliers);
@@ -106,7 +109,7 @@ int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
 	int ret;
 
 	mutex_lock(&fwnode_link_lock);
-	ret = __fwnode_link_add(con, sup);
+	ret = __fwnode_link_add(con, sup, 0);
 	mutex_unlock(&fwnode_link_lock);
 	return ret;
 }
@@ -126,6 +129,19 @@ static void __fwnode_link_del(struct fwnode_link *link)
 	kfree(link);
 }
 
+/**
+ * __fwnode_link_cycle - Mark a fwnode link as being part of a cycle.
+ * @link: the fwnode_link to be marked
+ *
+ * The fwnode_link_lock needs to be held when this function is called.
+ */
+static void __fwnode_link_cycle(struct fwnode_link *link)
+{
+	pr_debug("%pfwf: Relaxing link with %pfwf\n",
+		 link->consumer, link->supplier);
+	link->flags |= FWLINK_FLAG_CYCLE;
+}
+
 /**
  * fwnode_links_purge_suppliers - Delete all supplier links of fwnode_handle.
  * @fwnode: fwnode whose supplier links need to be deleted
@@ -199,7 +215,7 @@ static void __fwnode_links_move_consumers(struct fwnode_handle *from,
 	struct fwnode_link *link, *tmp;
 
 	list_for_each_entry_safe(link, tmp, &from->consumers, s_hook) {
-		__fwnode_link_add(link->consumer, to);
+		__fwnode_link_add(link->consumer, to, link->flags);
 		__fwnode_link_del(link);
 	}
 }
@@ -1041,6 +1057,21 @@ static bool dev_is_best_effort(struct device *dev)
 		(dev->fwnode && (dev->fwnode->flags & FWNODE_FLAG_BEST_EFFORT));
 }
 
+static struct fwnode_handle *fwnode_links_check_suppliers(
+						struct fwnode_handle *fwnode)
+{
+	struct fwnode_link *link;
+
+	if (!fwnode || fw_devlink_is_permissive())
+		return NULL;
+
+	list_for_each_entry(link, &fwnode->suppliers, c_hook)
+		if (!(link->flags & FWLINK_FLAG_CYCLE))
+			return link->supplier;
+
+	return NULL;
+}
+
 /**
  * device_links_check_suppliers - Check presence of supplier drivers.
  * @dev: Consumer device.
@@ -1068,11 +1099,8 @@ int device_links_check_suppliers(struct device *dev)
 	 * probe.
 	 */
 	mutex_lock(&fwnode_link_lock);
-	if (dev->fwnode && !list_empty(&dev->fwnode->suppliers) &&
-	    !fw_devlink_is_permissive()) {
-		sup_fw = list_first_entry(&dev->fwnode->suppliers,
-					  struct fwnode_link,
-					  c_hook)->supplier;
+	sup_fw = fwnode_links_check_suppliers(dev->fwnode);
+	if (sup_fw) {
 		if (!dev_is_best_effort(dev)) {
 			fwnode_ret = -EPROBE_DEFER;
 			dev_err_probe(dev, -EPROBE_DEFER,
@@ -1261,7 +1289,9 @@ static ssize_t waiting_for_supplier_show(struct device *dev,
 	bool val;
 
 	device_lock(dev);
-	val = !list_empty(&dev->fwnode->suppliers);
+	mutex_lock(&fwnode_link_lock);
+	val = !!fwnode_links_check_suppliers(dev->fwnode);
+	mutex_unlock(&fwnode_link_lock);
 	device_unlock(dev);
 	return sysfs_emit(buf, "%u\n", val);
 }
diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 89b9bdfca925..fdf2ee0285b7 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -18,7 +18,7 @@ struct fwnode_operations;
 struct device;
 
 /*
- * fwnode link flags
+ * fwnode flags
  *
  * LINKS_ADDED:	The fwnode has already be parsed to add fwnode links.
  * NOT_DEVICE:	The fwnode will never be populated as a struct device.
@@ -36,6 +36,7 @@ struct device;
 #define FWNODE_FLAG_INITIALIZED			BIT(2)
 #define FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD	BIT(3)
 #define FWNODE_FLAG_BEST_EFFORT			BIT(4)
+#define FWNODE_FLAG_VISITED			BIT(5)
 
 struct fwnode_handle {
 	struct fwnode_handle *secondary;
@@ -46,11 +47,19 @@ struct fwnode_handle {
 	u8 flags;
 };
 
+/*
+ * fwnode link flags
+ *
+ * CYCLE:	The fwnode link is part of a cycle. Don't defer probe.
+ */
+#define FWLINK_FLAG_CYCLE			BIT(0)
+
 struct fwnode_link {
 	struct fwnode_handle *supplier;
 	struct list_head s_hook;
 	struct fwnode_handle *consumer;
 	struct list_head c_hook;
+	u8 flags;
 };
 
 /**
-- 
2.39.1.519.gcb327c4b5f-goog