linux-kernel - [PATCH v2] base/platform: return success when probe function is NULL

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Date:	Mon, 30 Nov 2015 12:50:05 +0100
From:	martin.wilck@...fujitsu.com
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	u.kleine-koenig@...gutronix.de
Cc:	tpmdd-devel@...ts.sourceforge.net,
	Martin Wilck <Martin.Wilck@...fujitsu.com>
Subject: [PATCH v2] base/platform: return success when probe function is NULL

From: Martin Wilck <Martin.Wilck@...fujitsu.com>

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.

v2: fixed style issues, rephrased commit message.

Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")
Signed-off-by: Martin Wilck <Martin.Wilck@...fujitsu.com>
---
 drivers/base/platform.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 1dd6d3b..176b59f 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -513,10 +513,15 @@ 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) {
-- 
1.8.3.1

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