patch "base/platform: Fix platform drivers with no probe callback" added to driver-core-linus

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 my driver-core git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
in the driver-core-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

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

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(-)

index 73d6e5d39e33..f437afa17f2b 100644
@@ -558,10 +558,15 @@ static int platform_drv_probe(struct device *_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) {

2.7.0