Hi Marcel, > Am 18.08.2016 um 12:49 schrieb Marcel Holtmann <mar...@holtmann.org>: > > Hi Nikolaus, > >>> 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.
Yes, we can. But AFAIK no user space GPS client is expecting to have a new DEVTYPE. I have several different GPS devices. One is by bluetooth. So I get a /dev/tty through hci. Another one has an USB cable. I get a /dev/tty through some USB serial converter. A third one is integrated in a 4G modem which provides a /dev/ttyACM port. So I always get something which looks like a /dev/tty... Seems to be pretty standard. Yes it would be nice to have a /dev/gps2 device. And how do you want to control if the gps device should send records with cr / lf (INLCR, IGNCR)? Can you use tcsetattr? > > Such a driver then can also take care of the power control on open() and > close(). As it should be done in the first place. Yes it could do that as well. > And then we can also remove the RFKILL hacks for GPS devices as well. For > example that is what Intel and Broadcom Bluetooth devices do now. The power > control is hooked into hciconfig hci0 up/down. > > Regards > > Marcel > BR, Nikolaus
