On Thu, Aug 18, 2016 at 12:30:32PM +0200, Marcel Holtmann wrote: > 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. > > > > It should be. > > > >> - Split out the controller for uart_ports into separate driver. Do we see > >> a need for controller drivers that are not standard serial drivers? > > > > What do you mean by "controller" drivers here? I didn't understand them > > in the code. > > > >> - 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)? > > > > Why? Is the code as-is slow? > > > >> - Test with other UART drivers > >> - Convert a real driver/line discipline over to UART bus. > > > > That's going to be the real test, I recommend trying that as soon as > > possible as it will show where the real pain points are :) > > maybe we can get the Intel LnP driver ported over and see how that one > works out. It is one of the more complex ones when it comes to > bootloader and firmware loading. Maybe Loic can take a stab at this. > We would then also see how we can map the ACPI tables into a driver. Yes, I was going to complain about the OF-only bent of this patch, but I figured it would get fixed up once Rob started to use a "real" machine for his testing of this code :) > >> 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). > > > > Yes, I like the idea (minor nit, you still have SPMI in a lot of places > > instead of UART), so I recommend keeping going with it. > > > >> drivers/uart/Kconfig | 17 ++ > >> drivers/uart/Makefile | 3 + > >> drivers/uart/core.c | 458 +++++++++++++++++++++++++++++++++++++++ > >> drivers/uart/loopback.c | 72 ++++++ > > > > Why not just put this in drivers/tty/uart/ ? > > Is it really then a TTY at all. Would be the UART become the basic > core for a TTY? Hm, interesting idea. Not for all TTYs of course, but for those that are on UART devices, maybe? How would a usb-serial device fit into that picture? > Having tty/uart/ seems a bit backward. Then again, it is just a > directory name ;) And as we know, naming is hard :) thanks, greg k-h -- 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
