On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > SMBus slave configuration is activated by CFG_SEL[1:0]=0x1 pins > state. This is the mode the hub is supposed to be to let this driver > work correctly. But a race condition might happen right after reset > is cleared due to CFG_SEL[0] pin being multiplexed with SMBus SCL > function. In case if the reset pin is handled by a i2c GPIO expander, > which is also placed at the same i2c-bus segment as the usb251x > SMB-interface connected to, then the hub reset clearance might > cause the CFG_SEL[0] being latched in unpredictable state. So > sometimes the hub configuration mode might be 0x1 (as expected), > but sometimes being 0x0, which doesn't imply to have the hub SMBus-slave > interface activated and consequently causes this driver failure. > > In order to fix the problem we must make sure the GPIO-reset chip doesn't > reside the same i2c-bus segment as the SMBus-interface of the hub. If > it doesn't, we can safely block the segment for the time the reset is > cleared to prevent anyone generating a traffic at the i2c-bus SCL lane > connected to the CFG_SEL[0] pin. But if it does, nothing we can do, so > just return an error. If we locked the i2c-bus segment and tried to > communicate with the GPIO-expander, it would cause a deadlock. If we didn't > lock the i2c-bus segment, it would randomly cause the CFG_SEL[0] bit flip. > > Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> I signed off on this? Where? When? never add a s-o-b line that you did not create, that implies a legal agreement. greg k-h
