On Wed, Jun 20, 2018 at 07:17:53AM +0200, Peter Rosin wrote: > Hi! > > With the introduction of mux-locked I2C muxes, the concept of > locking only a segment of the I2C adapter tree was added. At the > time, I did not want to cause a lot of extra churn, so left most > users of i2c_lock_adapter alone and apparently didn't think enough > about it; they simply continued to lock the whole adapter tree. > However, i2c_lock_adapter is in fact wrong for almost every caller > (there is naturally an exception) that is itself not a driver for > a root adapter. What normal drivers generally want is to only > lock the segment of the adapter tree that their device sits on. > > In fact, if a device sits behind a mux-locked I2C mux, and its > driver calls i2c_lock_adapter followed by an unlocked I2C transfer, > things will deadlock (since even a mux-locked I2C adapter will lock > its parent at some point). If the device is not sitting behind a > mux-locked I2C mux (i.e. either directly on the root adapter or > behind a (chain of) parent-locked I2C muxes) the root/segment > distinction is of no consequence; the root adapter is locked either > way. > > Mux-locked I2C muxes are probably not that common, and putting any > of the affected devices behind one is probably even rarer, which > is why we have not seen any deadlocks. At least not that I know > of... > > Since silently changing the semantics of i2c_lock_adapter might > be quite a surprise, especially for out-of-tree users, this series > instead removes the function and forces all users to explicitly > name I2C_LOCK_SEGMENT or I2C_LOCK_ROOT_ADAPTER in a call to > i2c_lock_bus, as suggested by Wolfram. Yes, users will be a teensy > bit more wordy, but open-coding I2C locking from random drivers > should be avoided, so it's perhaps a good thing if it doesn't look > too neat? > > I suggest that Wolfram takes this series through the I2C tree and > creates an immutable branch for the other subsystems. The series > is based on v4.18-r1. Applied to a seperate branch named "i2c/precise-locking-names" which I will merge into for-next, so it will get proper testing already. Once we get the missing acks from media, MFD, and IIO maintainers, I will merge it into for-4.19. Thank you, Peter! -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
