linux-kernel - [PATCH] driver core: Avoid pointless deferred probe attempts

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Date:   Wed, 17 Feb 2021 15:51:30 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: [PATCH] driver core: Avoid pointless deferred probe attempts

There's no point in adding a device to the deferred probe list if we
know for sure that it doesn't have a matching driver. So, check if a
device can match with a driver before adding it to the deferred probe
list.

Signed-off-by: Saravana Kannan <saravanak@...gle.com>
---
Geert,

Can you give this a shot for your I2C DMA issue with fw_devlink=on?

-Saravana

 drivers/base/dd.c      | 6 ++++++
 include/linux/device.h | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9179825ff646..f18963f42e21 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -123,6 +123,9 @@ static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
 
 void driver_deferred_probe_add(struct device *dev)
 {
+	if (!dev->can_match)
+		return;
+
 	mutex_lock(&deferred_probe_mutex);
 	if (list_empty(&dev->p->deferred_probe)) {
 		dev_dbg(dev, "Added to deferred list\n");
@@ -726,6 +729,7 @@ static int driver_probe_device(struct device_driver *drv, struct device *dev)
 	if (!device_is_registered(dev))
 		return -ENODEV;
 
+	dev->can_match = true;
 	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 
@@ -829,6 +833,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
 		return 0;
 	} else if (ret == -EPROBE_DEFER) {
 		dev_dbg(dev, "Device match requests probe deferral\n");
+		dev->can_match = true;
 		driver_deferred_probe_add(dev);
 	} else if (ret < 0) {
 		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
@@ -1064,6 +1069,7 @@ static int __driver_attach(struct device *dev, void *data)
 		return 0;
 	} else if (ret == -EPROBE_DEFER) {
 		dev_dbg(dev, "Device match requests probe deferral\n");
+		dev->can_match = true;
 		driver_deferred_probe_add(dev);
 	} else if (ret < 0) {
 		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
diff --git a/include/linux/device.h b/include/linux/device.h
index 7619a84f8ce4..1f9cc1ba78bc 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -438,6 +438,9 @@ struct dev_links_info {
  * @state_synced: The hardware state of this device has been synced to match
  *		  the software state of this device by calling the driver/bus
  *		  sync_state() callback.
+ * @can_match:	The device has matched with a driver at least once or it is in
+ *		a bus (like AMBA) which can't check for matching drivers until
+ *		other devices probe successfully.
  * @dma_coherent: this particular device is dma coherent, even if the
  *		architecture supports non-coherent devices.
  * @dma_ops_bypass: If set to %true then the dma_ops are bypassed for the
@@ -544,6 +547,7 @@ struct device {
 	bool			offline:1;
 	bool			of_node_reused:1;
 	bool			state_synced:1;
+	bool			can_match:1;
 #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
-- 
2.30.0.478.g8a0d178c01-goog