Patch "base/platform: Fix platform drivers with no probe callback" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

base/platform: Fix platform drivers with no probe callback

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
base-platform-fix-platform-drivers-with-no-probe-callback.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Martin Wilck <[email protected]>
Date: Mon, 30 Nov 2015 12:50:05 +0100
Subject: base/platform: Fix platform drivers with no probe callback

From: Martin Wilck <[email protected]>

commit 25cad69f21f5532d99e2ee73c8ab6512bcab614c upstream.

Since b8b2c7d845d5, platform_drv_probe() is called for all platform devices. If drv->probe is NULL, and dev_pm_domain_attach() fails, platform_drv_probe() will return the error code from dev_pm_domain_attach().

This causes real_probe() to enter the "probe_failed" path and set dev->driver to NULL. Before b8b2c7d845d5, real_probe() would assume success if both dev->bus->probe and drv->probe were missing. As a result, a device and driver could be "bound" together just by matching their names; this doesn't work any more after b8b2c7d845d5.

This may cause problems later for certain usage of platform_driver_register() and platform_device_register_simple(). I observed a panic while loading the tpm_tis driver with parameter "force=1" (i.e. registering tpm_tis as a platform driver), because tpm_tis_init's assumption that the device returned by platform_device_register_simple() was bound didn't hold any more (tpmm_chip_alloc() dereferences chip->pdev->driver, causing panic).

This patch restores the previous (4.3.0 and earlier) behavior of platform_drv_probe() in the case when the associated platform driver has no "probe" function.

---
 drivers/base/platform.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

@@ -513,10 +513,15 @@ static int platform_drv_probe(struct dev
 		return ret;
 
 	ret = dev_pm_domain_attach(_dev, true);
-	if (ret != -EPROBE_DEFER && drv->probe) {
-		ret = drv->probe(dev);
-		if (ret)
-			dev_pm_domain_detach(_dev, true);
+	if (ret != -EPROBE_DEFER) {
+		if (drv->probe) {
+			ret = drv->probe(dev);
+			if (ret)
+				dev_pm_domain_detach(_dev, true);
+		} else {
+			/* don't fail if just dev_pm_domain_attach failed */
+			ret = 0;
+		}
 	}
 
 	if (drv->prevent_deferred_probe && ret == -EPROBE_DEFER) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/base-platform-fix-platform-drivers-with-no-probe-callback.patch