Hi, On Thu, Aug 18, 2016 at 06:08:24PM -0500, Rob Herring wrote: > On Thu, Aug 18, 2016 at 3:29 PM, Sebastian Reichel <sre@xxxxxxxxxx> wrote: > > 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? Nokia's bluetooth uart protocol disables flow control during speed changes. > > 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 meant "Either some function similar to userspace's poll() is needed, ...". Something like uart_dev_wait_for_rx() Alternatively the rx function could be a callback, that is called when there is new data. > I'm assuming the only immediate consumers are in-kernel. Yes, but the driver should be notified about incoming data. -- Sebastian
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