On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > 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. > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > since you already added the first version of this into linux-next tree. But > apparently copy-pasted and left as is... If I have already applied a patch, I can't apply it again (or a different version.) You need to send a fix-up patch for the reported issue, not a whole new one as I can not go back in time and rewrite history. thanks, greg k-h
