fix hotplug for legacy platform drivers

We've had various reports of some legacy "probe the hardware" style
platform drivers having nasty problems with hotplug support.

The core issue is that those legacy drivers don't fully conform to the
driver model.  They assume a role that should be the responsibility of
infrastructure code: creating device nodes.

The "modprobe" step in hotplugging relies on drivers to have split those
roles into different modules.  The lack of this split causes the problems.
When a driver creates nodes for devices that don't exist (sending a hotplug
event), then exits (aborting one modprobe) before the "modprobe $MODALIAS"
step completes (by failing, since it's in the middle of a modprobe), the
result can be an endless loop of modprobe invocations ...  badness.

This fix uses the newish per-device flag controlling issuance of "add"
events.  (A previous version of this patch used a per-device "driver can
hotplug" flag, which only scrubbed $MODALIAS from the environment rather
than suppressing the entire hotplug event.) It also shrinks that flag to
one bit, saving a word in "struct device".

So the net of this patch is removing some nasty failures with legacy
drivers, while retaining hotplug capability for the majority of platform
drivers.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Greg KH <gregkh@suse.de>
Cc: Andres Salomon <dilinger@debian.org>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 17b5ece8f82c..eb84d9d44645 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -160,6 +160,11 @@ static void platform_device_release(struct device *dev)
  *
  *      Create a platform device object which can have other objects attached
  *      to it, and which will have attached objects freed when it is released.
+ *
+ *      This device will be marked as not supporting hotpluggable drivers; no
+ *      device add/remove uevents will be generated.  In the unusual case that
+ *      the device isn't being dynamically allocated as a legacy "probe the
+ *      hardware" driver, infrastructure code should reverse this marking.
  */
 struct platform_device *platform_device_alloc(const char *name, unsigned int id)
 {
@@ -172,6 +177,12 @@ struct platform_device *platform_device_alloc(const char *name, unsigned int id)
                 pa->pdev.id = id;
                 device_initialize(&pa->pdev.dev);
                 pa->pdev.dev.release = platform_device_release;
+
+                /* prevent hotplug "modprobe $(MODALIAS)" from causing trouble in
+                 * legacy probe-the-hardware drivers, which don't properly split
+                 * out device enumeration logic from drivers.
+                 */
+                pa->pdev.dev.uevent_suppress = 1;
         }
 
         return pa ? &pa->pdev : NULL;
@@ -351,6 +362,13 @@ EXPORT_SYMBOL_GPL(platform_device_unregister);
  *      memory allocated for the device allows drivers using such devices
  *      to be unloaded iwithout waiting for the last reference to the device
  *      to be dropped.
+ *
+ *      This interface is primarily intended for use with legacy drivers
+ *      which probe hardware directly.  Because such drivers create sysfs
+ *      device nodes themselves, rather than letting system infrastructure
+ *      handle such device enumeration tasks, they don't fully conform to
+ *      the Linux driver model.  In particular, when such drivers are built
+ *      as modules, they can't be "hotplugged".
  */
 struct platform_device *platform_device_register_simple(char *name, unsigned int id,
                                                         struct resource *res, unsigned int num)