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); 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. -- Sebastian
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