Hi Greg, >>>>>> Currently, devices attached via a UART are not well supported in the >>>>>> kernel. The problem is the device support is done in tty line disciplines, >>>>>> various platform drivers to handle some sideband, and in userspace with >>>>>> utilities such as hciattach. >>>>>> >>>>>> There have been several attempts to improve support, but they suffer from >>>>>> still being tied into the tty layer and/or abusing the platform bus. This >>>>>> is a prototype to show creating a proper UART bus for UART devices. It is >>>>>> tied into the serial core (really struct uart_port) below the tty layer >>>>>> in order to use existing serial drivers. >>>>>> >>>>>> This is functional with minimal testing using the loopback driver and >>>>>> pl011 (w/o DMA) UART under QEMU (modified to add a DT node for the slave >>>>>> device). It still needs lots of work and polish. >>>>>> >>>>>> TODOs: >>>>>> - Figure out the port locking. mutex plus spinlock plus refcounting? I'm >>>>>> hoping all that complexity is from the tty layer and not needed here. >>>>>> - Split out the controller for uart_ports into separate driver. Do we see >>>>>> a need for controller drivers that are not standard serial drivers? >>>>>> - Implement/test the removal paths >>>>>> - Fix the receive callbacks for more than character at a time (i.e. DMA) >>>>>> - Need better receive buffering than just a simple circular buffer or >>>>>> perhaps a different receive interface (e.g. direct to client buffer)? >>>>>> - Test with other UART drivers >>>>>> - Convert a real driver/line discipline over to UART bus. >>>>>> >>>>>> Before I spend more time on this, I'm looking mainly for feedback on the >>>>>> general direction and structure (the interface with the existing serial >>>>>> drivers in particular). >>>>> >>>>> Some quick comments (can't do any real life tests in the next weeks) from my (biased) view: >>>>> >>>>> * tieing the solution into uart_port is the same as we had done. The difference seems to >>>>> me that you completely bypass serial_core (and tty) while we want to integrate it with standard tty operation. >>>>> >>>>> We have tapped the tty layer only because it can not be 100% avoided if we use serial_core. >>>>> >>>>> * one feedback I had received was that there may be uart device drivers not using serial_core. I am not sure if your approach addresses that. >>>>> >>>>> * what I don't see is how we can implement our GPS device power control driver: >>>>> - the device should still present itself as a tty device (so that cat /dev/ttyO1 reports NMEA records) and should >>>>> not be completely hidden from user space or represented by a new interface type invented just for this device >>>>> (while the majority of other GPS receivers are still simple tty devices). >>>>> - how we can detect that the device is sending data to the UART while no user space process has the uart port open >>>>> i.e. when does the driver know when to start/stop the UART. >>>> >>>> I am actually not convinced that GPS should be represented as >>>> /dev/ttyS0 or similar TTY. It think they deserve their own driver >>>> exposing them as simple character devices. That way we can have a >>>> proper DEVTYPE and userspace can find them correctly. We can also >>>> annotate them if needed for special settings. >>> >>> I would _love_ to see that happen, but what about the GPS line >>> discipline that we have today? How would that match up with a char >>> device driver? >> >> we have a GPS line discipline? What is that one doing? As far as I >> know all GPS implementations are fully userspace. > > Hm, for some reason I thought that was what n_gsm.c was being used for, > but I could be wrong, I've never seen the hardware that uses that > code... the n_gsm.c is for 3GPP TS 07.10. Which is a TTY multiplexer. Has nothing to do with GPS. Regards Marcel -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
