In drm we've added nice drm_device (the main gpu driver thing, which also represents the userspace interfaces and has everything else dangling off it) init functions using devres, devm_drm_dev_init and soon devm_drm_dev_alloc (this patch series adds that).
A slight trouble is that drm_device itself holds a reference on the struct device it's sitting on top (for sysfs links and dmesg debug and lots of other things), so there's a reference loop. For real drivers this is broken at remove/unplug time, where all devres resources are released device_release_driver(), before the final device reference is dropped. So far so good.
There's 2 exceptions: - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual platform device to make them look more like normal devices to userspace. These aren't drivers in the driver model sense, we simple create a platform_device and register it.
- drm/i915/selftests, where we create minimal mock devices, and again the selftests aren't proper drivers in the driver model sense.
For these two cases the reference loop isn't broken, because devres is only cleaned up when the last device reference is dropped. But that's not happening, because the drm_device holds that last struct device reference.
Thus far this wasn't a problem since the above cases simply hand-rolled their cleanup code. But I want to convert all drivers over to the devm_ versions, hence it would be really nice if these virtual/fake/mock uses-cases could also be managed with devres cleanup.
I see three possible approaches:
- Clean up devres from device_del (or platform_device_unregister) even when no driver is bound. This seems like the simplest solution, but also the one with the widest impact, and what this patch implements. We might want to include more of the cleanup than just devres_release_all, but this is all I need to get my use case going.
- Create a devres group and release that when we unbind. The code in virtual drivers gets a bit ugly, since every error case has a different cleanup code until we've chained everything (platform_device, devres group and then drm_device) together and a devres_release_group takes care of everything. Doable, but a bit confusing when I typed it out.
- Convert the virtual drivers to real (in the device model sense) drivers. Feels like too much boilerplate for not much gain. And especially with the mock objects minimal mocking is kinda the goal, to limit the amount of accidentally pulled in code into our unit tests as much as possible.
Either way I think time to discuss this a bit and figure out what's the recommended approach here.
Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: "Rafael J. Wysocki" rafael@kernel.org --- drivers/base/dd.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/base/dd.c b/drivers/base/dd.c index b25bcab2a26b..1bcfb0ff5f44 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -1155,6 +1155,8 @@ static void __device_release_driver(struct device *dev, struct device *parent) dev);
kobject_uevent(&dev->kobj, KOBJ_UNBIND); + } else { + devres_release_all(dev); } }