On Fri, 17 May 2013, Alexander Sverdlin wrote: > Hi! > > On 05/17/2013 04:42 PM, ext Alan Stern wrote: > >> i2c: suppress lockdep warning on delete_device > >> > >> Since commit 846f99749ab68bbc7f75c74fec305de675b1a1bf the following lockdep > >> warning is thrown in case i2c device is removed (via delete_device sysfs > >> attribute) which contains subdevices (e.g. i2c multiplexer): > > > > Can you explain this in a little more detail? Exactly what does the > > delete_device attribute do, when called for device D? > > > > That is, what does a write to /sys/bus/i2c/devices/D/delete_device do? > > Like USB with its hubs, I2C structure could be tree-like, with I2C multiplexers. > delete_device attribute removes I2C device from the subsystem, which is usually not > a problem, except the case when device is a multiplexer and sub-devices should be > removed first. Here we have the problem: holding a "s_active" lock on > "delete_device" attribute of a parent (multiplexer) we need to delete children, but > they were created with the same static attribute "delete_device". > > The safety of this operation is exactly the same as in USB case... Any more clever > lockdep annotation is exactly not so easy... If I understand you correctly, if D is an I2C multiplexer then writing to /sys/bus/i2c/devices/D/delete_device will get rid of all of D's children (and their descendants) and will also get rid of D itself -- right? That's _not_ what the USB attributes do. For example, if D is a USB hub then writing 0 to /sys/bus/usb/devices/D/bConfigurationValue will get rid of all D's descendants but will not get rid of D. Instead of doing it this way, the attribute method should call device_schedule_callback(). See commit d9a9cdfb078d. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
