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Sender: "saravanak via sendgmr" <saravanak@saravanak.san.corp.google.com>
Date:   Tue,  2 Mar 2021 13:11:30 -0800
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Subject: [PATCH v1 1/3] driver core: Avoid pointless deferred probe attempts
From:   Saravana Kannan <saravanak@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Saravana Kannan <saravanak@google.com>,
        Michael Walle <michael@walle.cc>,
        Jon Hunter <jonathanh@nvidia.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Guenter Roeck <linux@roeck-us.net>, kernel-team@android.com,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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@google.com>
---
 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 ba660731bd25..569932d282c0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -439,6 +439,9 @@ 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
@@ -545,6 +548,7 @@ 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)
-- 
2.30.1.766.gb4fecdf3b7-goog