On Sun, 8 Sep 2002 phil at netroedge.com wrote: > > Just to throw my $.02 in, I think Kyosti is right to say the problem > isn't really ideally fixed, however we've made some significant > progress in making it fairly safe for known users with this chip. Agreed. > As far as adding locking goes, I can't think of a reason why we need > locking to implement the I2C/SMBus protocol. It would be the safest > way to go to implement a completely reliable workaround for this > particular issue, but is it *right*? Unless we are going to need this > locking mechanism as a standard feature, I would opt to not implement > it. Are there are any other devices which require that consecutive > transations (not just with it, but all bus transactions) to be tightly > controlled? Do we have reason to believe that there may be more in > the future? The special Start and Stop sequences quarantee mutual exclusion even on multi-master buses. Eg. Read Byte/Word sequences do not send Stop between selecting register and reading contents. There should be no need to promote further bus locking for user-space. > The nice thing with putting drivers in the kernel is that we can allow > everyone access to the bus w/o the risk of someone hogging control of > it. If we add locking, we potentially lose that if a user-space app > abuses the locking feature. I agree. However I do not consider current situation very satisfactory: 1. Blacklisting by DMI data does not catch new models beforehand. 2. IBM systems with other than PIIX4 are compromised if admin does not run and/or believe sensors-detect warnings and is unaware of the issue. 3. If #1 or #2 happens, every existing client driver probing around 0x54-0x57 needs a workaround. Including video4linux(2) drivers from several sources, and any app using the char device. I think patching i2c-core to add extra Write Quick within the critical section is safe and easy way to handle those issues. This leaves only multi-master topologies vulnerable. What do the SMBus specs say, can a laptop share SMBus with a docking station, charger etc ? -- Ky?sti M?lkki kmalkki at cc.hut.fi
