On Thu, Aug 18, 2016 at 3:29 PM, Sebastian Reichel <s...@kernel.org> wrote: > Hi Rob, > > Thanks for going forward and implementing this. I also started, > but was far from a functional state. > > On Wed, Aug 17, 2016 at 08:14:42PM -0500, Rob Herring wrote: >> 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). > > I had a look at the uart_dev API: > > int uart_dev_config(struct uart_device *udev, int baud, int parity, int bits, > int flow); > int uart_dev_connect(struct uart_device *udev); > > The flow control configuration should be done separately. e.g.: > uart_dev_flow_control(struct uart_device *udev, bool enable);
No objection, but out of curiosity, why? > int uart_dev_tx(struct uart_device *udev, u8 *buf, size_t count); > int uart_dev_rx(struct uart_device *udev, u8 *buf, size_t count); > > UART communication does not have to be host-initiated, so this > API requires polling. Either some function similar to poll in > userspace is needed, or it should be implemented as callback. What's the userspace need? I'm assuming the only immediate consumers are in-kernel. Rob
