[PATCH 03/17] net: phy: Attach generic PHY drivers through the driver core

[Leon Romanovsky]

From: Leon Romanovsky <leonro@xxxxxxxxxx>

The generic PHY fallback probes directly before publishing its binding,
bypassing driver-core admission and supplier checks.

Attach through the driver core so admission precedes functional setup.
Callers hold RTNL, which a concurrent bind of a specific driver may wait
for with the device lock held, so for this flow let's add
device_driver_try_attach() so the attachment never waits for that lock.

Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
 drivers/base/dd.c            | 65 +++++++++++++++++++++++++++++++++++++-------
 drivers/net/phy/phy_device.c | 39 +++++++++++++++++---------
 include/linux/device.h       |  2 ++
 3 files changed, 83 insertions(+), 23 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 52123251965de..01026e02de92e 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1046,6 +1046,25 @@ static void __device_driver_lock(struct device *dev, struct device *parent)
 	device_lock(dev);
 }
 
+/*
+ * __device_driver_trylock - __device_driver_lock() without sleeping
+ *
+ * Returns true if the locks were taken.
+ */
+static bool __device_driver_trylock(struct device *dev, struct device *parent)
+{
+	if (dev->type && dev->type->need_parent_lock && parent) {
+		if (!device_trylock(parent))
+			return false;
+		if (!device_trylock(dev)) {
+			device_unlock(parent);
+			return false;
+		}
+		return true;
+	}
+	return device_trylock(dev);
+}
+
 /*
  * __device_driver_unlock - release locks needed to manipulate dev->drv
  * @dev: Device we will update driver info for
@@ -1195,19 +1214,17 @@ void device_initial_probe(struct device *dev)
 	subsys_put(sp);
 }
 
-/**
- * device_driver_attach - attach a specific driver to a specific device
- * @drv: Driver to attach
- * @dev: Device to attach it to
- *
- * Manually attach driver to a device. Will acquire both @dev lock and
- * @dev->parent lock if needed. Returns 0 on success, -ERR on failure.
- */
-int device_driver_attach(const struct device_driver *drv, struct device *dev)
+static int __device_driver_attach(const struct device_driver *drv,
+				  struct device *dev, bool trylock)
 {
 	int ret;
 
-	__device_driver_lock(dev, dev->parent);
+	if (trylock) {
+		if (!__device_driver_trylock(dev, dev->parent))
+			return -EBUSY;
+	} else {
+		__device_driver_lock(dev, dev->parent);
+	}
 	ret = __driver_probe_device(drv, dev);
 	__device_driver_unlock(dev, dev->parent);
 
@@ -1218,8 +1235,36 @@ int device_driver_attach(const struct device_driver *drv, struct device *dev)
 		return -EAGAIN;
 	return ret;
 }
+
+/**
+ * device_driver_attach - attach a specific driver to a specific device
+ * @drv: Driver to attach
+ * @dev: Device to attach it to
+ *
+ * Manually attach driver to a device. Will acquire both @dev lock and
+ * @dev->parent lock if needed. Returns 0 on success, -ERR on failure.
+ */
+int device_driver_attach(const struct device_driver *drv, struct device *dev)
+{
+	return __device_driver_attach(drv, dev, false);
+}
 EXPORT_SYMBOL_GPL(device_driver_attach);
 
+/**
+ * device_driver_try_attach - attach a specific driver without waiting for locks
+ * @drv: Driver to attach
+ * @dev: Device to attach it to
+ *
+ * Like device_driver_attach(), for callers that hold a lock which the holder
+ * of the @dev or @dev->parent lock may wait for. Returns -EBUSY, before any
+ * probing, if one of those locks is contended.
+ */
+int device_driver_try_attach(const struct device_driver *drv, struct device *dev)
+{
+	return __device_driver_attach(drv, dev, true);
+}
+EXPORT_SYMBOL_GPL(device_driver_try_attach);
+
 static void __driver_attach_async_helper(void *_dev, async_cookie_t cookie)
 {
 	struct device *dev = _dev;
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 5d4508bcfbe99..8cc0de755bd08 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1912,7 +1912,9 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	struct device *d = &phydev->mdio.dev;
 	struct module *ndev_owner = NULL;
 	struct module *drv_owner;
+	struct device_driver *drv;
 	int irq = phydev->irq;
+	bool bind_genphy;
 	int err;
 
 	/* For Ethernet device drivers that register their own MDIO bus, we
@@ -1939,16 +1941,16 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	/* Assume that if there is no driver, that it doesn't
 	 * exist, and we should use the genphy driver.
 	 */
-	if (!d->driver) {
+	drv = d->driver;
+	bind_genphy = !drv;
+	if (bind_genphy) {
 		if (phydev->is_c45)
-			d->driver = &genphy_c45_driver.mdiodrv.driver;
+			drv = &genphy_c45_driver.mdiodrv.driver;
 		else
-			d->driver = &genphy_driver.mdiodrv.driver;
-
-		phydev->is_genphy_driven = 1;
+			drv = &genphy_driver.mdiodrv.driver;
 	}
 
-	drv_owner = d->driver->owner;
+	drv_owner = drv->owner;
 	if (!try_module_get(drv_owner)) {
 		phydev_err(phydev, "failed to get the device driver module\n");
 		err = -EIO;
@@ -1956,11 +1958,20 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	}
 	phydev->drv_owner = drv_owner;
 
-	if (phydev->is_genphy_driven) {
-		err = d->driver->probe(d);
-		if (err >= 0)
-			err = device_bind_driver(d);
-
+	if (bind_genphy) {
+		/*
+		 * RTNL is held, and a concurrent bind of a specific driver may
+		 * wait for it with the device lock held. Never wait for that
+		 * lock, and let the caller retry.
+		 */
+		err = device_driver_try_attach(drv, d);
+		if (err == -EBUSY) {
+			/* Another bind owns the PHY, so nothing was probed here. */
+			irq = phydev->irq;
+			err = -EPROBE_DEFER;
+		} else if (err == -EAGAIN) {
+			err = -EPROBE_DEFER;
+		}
 		if (err)
 			goto error_module_put;
 	}
@@ -2071,8 +2082,6 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	module_put(phydev->drv_owner);
 	phydev->drv_owner = NULL;
 	phydev->irq = irq;
-	phydev->is_genphy_driven = 0;
-	d->driver = NULL;
 error_put_device:
 	put_device(d);
 	if (ndev_owner != bus->owner)
@@ -3813,6 +3822,8 @@ static int phy_probe(struct device *dev)
 	int err = 0;
 
 	phydev->drv = phydrv;
+	phydev->is_genphy_driven = phydrv == &genphy_driver ||
+				 phydrv == &genphy_c45_driver;
 
 	/* Disable the interrupt if the PHY doesn't support it
 	 * but the interrupt is still a valid one
@@ -3949,6 +3960,7 @@ static int phy_probe(struct device *dev)
 out_reset:
 	/* Re-assert the reset signal on error */
 	phy_device_reset(phydev, 1);
+	phydev->is_genphy_driven = 0;
 
 	return err;
 }
@@ -3977,6 +3989,7 @@ static int phy_remove(struct device *dev)
 	phy_device_reset(phydev, 1);
 
 	phydev->drv = NULL;
+	phydev->is_genphy_driven = 0;
 
 	return 0;
 }
diff --git a/include/linux/device.h b/include/linux/device.h
index 429e39f647cf9..4cf62d69eac4f 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1314,6 +1314,8 @@ static inline void *dev_get_platdata(const struct device *dev)
  */
 int __must_check device_driver_attach(const struct device_driver *drv,
 				      struct device *dev);
+int __must_check device_driver_try_attach(const struct device_driver *drv,
+					  struct device *dev);
 int __must_check device_bind_driver(struct device *dev);
 void device_release_driver(struct device *dev);
 int  __must_check device_attach(struct device *dev);

-- 
2.56.0