On Mon, Aug 19, 2024 at 09:19:10AM +0200, Stefan Eichenberger wrote: > From: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx> > > We are experiencing a problem with the i.MX I2C controller when > communicating with SMBus devices. We are seeing devices time-out because > the time between sending/receiving two bytes is too long, and the SMBus > device returns to the idle state. This happens because the i.MX I2C > controller sends and receives byte by byte. When a byte is sent or > received, we get an interrupt and can send or receive the next byte. > > The current implementation sends a byte and then waits for an event > generated by the interrupt subroutine. After the event is received, the > next byte is sent and we wait again. This waiting allows the scheduler > to reschedule other tasks, with the disadvantage that we may not send > the next byte for a long time because the send task is not immediately > scheduled. For example, if the rescheduling takes more than 25ms, this > can cause SMBus devices to timeout and communication to fail. > > This patch changes the behavior so that we do not reschedule the > send/receive task, but instead send or receive the next byte in the > interrupt subroutine. This prevents rescheduling and drastically reduces > the time between sending/receiving bytes. The cost in the interrupt > subroutine is relatively small, we check what state we are in and then > send/receive the next byte. Before we had to call wake_up, which is even > less expensive. However, we also had to do some scheduling, which > increased the overall cost compared to the new solution. The wake_up > function to wake up the send/receive task is now only called when an > error occurs or when the transfer is complete. > > Signed-off-by: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx> Acked-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
