Hello Peter, Thank you for your feedback! > > The "mux-locked" implementation was the one I first tried and I discovered > > it doesn't work for me, as other traffic on the parent adapter can get in the > > way. What we need for this device is no other traffic on the bus during the > > "select transaction deselect" procedure, that's why I went with the parent > > locking. Also this device needs a delay between stop and start conditions > > while addressing the monitor. > > Ok, I thought the problem was that a delay was needed between the STOP > of the command opening the gate and the START of the edid eeprom xfer, and > that everything else worked normally. Too bad this wasn't the actual problem. > > Hmm. If it is indeed true that other xfers must never creep into the "select > xfer deselect" procedure then you are indeed stuck with a parent-locking. > But is that really the case? Could it be that the extra delay between > STOP-START is only needed after the absolutely last xfer before the > command closing the gate? > > If that problem description is correct, it should be possible to go back to > a mux-locked gate, but then in your deselect implementation grab the i2c adapter > lock manually - with i2c_lock_bus(adapter, I2C_LOCK_ROOT_ADAPTER) - before the > 30 us delay, then open code the command to close the gate with an unlocked i2c > access, and finally release the i2c bus lock. That way you have ensured silence > on the bus for the required time before closing the gate. You would still need > to bypass regmap, but only in this one place (but maybe you should bypass > regmap for opening the gate too, for symmetry). To further detail the problem, the system is vulnerable from before the last write performed by sii902x_i2c_bypass_select to after we confirm we need the switch to be closed within sii902x_i2c_bypass_deselect, that's the minimum amount of time we could keep the parent adapter locked for, I guess I am stuck with a parent-locking architecture, aren't I? But I guess I could release it when it's not actually needed, or is this going to be a pain to maintain? Shall I just keep going with the parent-locking but using bare i2c transactions only within select and deselect and leave regmap to deal with everything else? snip > > > > Ah, do you think the following is going to cause any issue in the future? > > -edid = drm_get_edid(connector, sii902x->i2c->adapter); > > +edid = drm_get_edid(connector, sii902x->i2cmux->adapter[0]); > > No, that was a critical part of the idea to use a gate to introduce the > needed delay. Again, thank you very much for spending your time looking into this, your feedback is very much appreciated. Fab > > Cheers, > Peter Renesas Electronics Europe Ltd, Dukes Meadow, Millboard Road, Bourne End, Buckinghamshire, SL8 5FH, UK. Registered in England & Wales under Registered No. 04586709.
