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. 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
