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.

Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")
Signed-off-by: Martin Wilck <Martin.Wilck@ts.fujitsu.com>
Cc: stable <stable@vger.kernel.org> # 4.4
Cc: Martin Fuzzey <mfuzzey@parkeon.com>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 4 deletions

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 73d6e5d39e33..f437afa17f2b 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -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) {