Hi Jean, On 25-07-16, 11:39, Jean Delvare wrote: > The problem is that the patch proposed by Viresh has nothing to do with > this. It's not adding notifications, just changing the time frame during > which user-space holds a reference to the i2c (bus) device. The goal as > I understand it is to allow *prepared* hot-unplug (in the form of > "rmmod i2c-bus-device-driver" or sysfs-based offlining?) while Not really. We are concerned about both prepared and Unprepared cases. This *hacky* patch was useful in case of *unprepared* hot-unplug as well. Here is the sequence of events: - open() i2c device from userspace - do some operations on the device read/write/ioctls() .. - Module hot-unplugged (*unprepared*) - Some of the ongoing i2c transactions may just fail, that is fine .. - Kernel detected the interrupt about module removal and tries to cleanup the devices.. - Now, kernel can not remove the i2c device, unless user application has closed the file descriptor. And so kernel is waiting in the driver's ->remove() callback forever. Also, there is no way to co-ordinate (in Android) with the Applications using the device. They can crash or fail out if they want to, but the kernel shouldn't stop removal of a hardware module in that case. > user-space processes have i2c device nodes open. Unprepared hot-unplug > will still go wrong exactly as it goes now. > My point is that prepared hot-unplug can already be achieved today > without any patch. Yeah, if we have the option of stopping the applications before the device is gone. > Or possibly improved by adding a notification > mechanism. But not by changing the reference holding design. > > Not only the proposed patch does not help and degrades the performance, > but it breaks assumptions. For example, it would allow an application > to open an i2c bus, then you remove its driver and load another i2c bus > driver, which gets the same bus number, and now the application writes > to a completely different I2C bus segment. The current reference model > prevents that, on purpose. > > So, again, nack from me. Yeah, the patch wasn't great and I knew it from the beginning. But we are looking for a solution that can be accepted and so need advice from you guys :) -- viresh -- 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
