On Mon, 28 Nov 2011 10:51:59 +0100 Michael Lawnick <ml.lawnick@xxxxxx> wrote: > Am 28.11.2011 08:48, schrieb David Jander: > > > > Hi Micheal, > > > > On Fri, 25 Nov 2011 11:27:44 +0100 > > Michael Lawnick <ml.lawnick@xxxxxx> wrote: > >> Am 24.11.2011 12:02, schrieb David Jander: > >>> For many peripherals in order to support this, a special function would > >>> be needed, that reconfigures the SDA/SCL pins as GPIO and manually > >>> toggles SCL a few times. This would probably need to be implemented in > >>> board-support-/platform code...? > >> > >> Needs to be part of recover function which in turn is part of driver code. > > > > In the case of the i.MX I2C peripheral, and probably in the case of a few > > others, there is no way of doing this, except for switching I2C i/o pins to > > GPIO via the iomux and toggling the GPIO pin that corresponds to SCL "by > > hand", while watching the GPIO pin that corresponds to SDA. > > So only one problem up to here: may the i2c adapter code have reserved > access to iomux? If its the only user -> move control into adpater > driver, reserve the H/W-access and you are done. If not, then you have a > shared device -> make a driver for iomux registers that serializes > access, possibly with reservation functions, export them and reference > from adapter code. I don't think IOMUX should ever be accessed directly within a driver. Besides, the imx-i2c.c peripheral is found in many different chips that have the same I2C controller, but different IOMUX and GPIO peripherals. I think, what we are missing is probably a generic IOMUX framework for linux, that can deal with changing functions of I/O pins. Until we have such a framework, we probably must do with platform-data function-pointers.... :-( I would like to know if anyone disagrees with the fact that I2C bus fault recovery and reset should be done by the driver. If no one disagrees, I will try to add support for this to the imx-i2c.c driver. > >>> In my specific situation, there was no way of recovering other than > >>> power-cycling the device, which is completely unacceptable, specially for > >>> an industrial control system. A temporary bus-lockup with automatic > >>> recovery via a proper I2C bus reset OTOH, wouldn't have any significant > >>> impact even if occurring sporadically. > >>> Individually resetting I2C slaves is also not a real solution because it > >>> may not be possible to determine which is the I2C slave that misbehaved. > >> > >> Most I2C slaves haven't got any reset line. > > > > Even worse.... that means the bus will never come back, even if you reset > > the machine!!! Only a power-cycle would save you. > > > Correct. > > >>> Any idea on how to solve this problem? > >>> Should each driver implement support for it and implement optional > >>> callback functions in platform-data? > >> > >> IMHO this typically is adapter driver's job. It strongly depends on > >> particular H/W whether controller can return information on busy/blocked > >> bus and whether it is able to manually toggle the clock line. On single > >> master systems, the driver code should automatically try to recover when > >> not being able to send start flag. On multi master systems the situation > >> is more complex. > > > > I agree. There might be a few platforms where there is no solution to this, > > other than hardwiring a separate GPIO line to SCL... > > or by wiring Vcc of unresetable I2C devices to a controllable on-board > power supply/relays. Yes, but that would be more or less like having a reset-pin on the device... :-) Best regards, -- David Jander Protonic Holland. -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
