On 13/08/13 21:12, Andrew Ruder wrote: > Sorry for the late reply, I've been thinking about this for some time > and was sad to see it didn't really evoke any sort of discussion :(. > > On Sat, Aug 10, 2013 at 02:58:08PM +0100, Mark Jackson wrote: >> When a UART transmitter is connected to (eg) a RS485 driver, it is >> necessary to turn the driver on/off as quickly as possible. This is >> best achieved in the serial driver itself (rather than in userspace >> where the latency can be quite large). >> >> This patch allows the GPIO pin to be defined (via DT) that controls >> the enabling of the driver at the start of a message, and disables >> the driver when the message has been completed. >> >> Still to do:- >> Allow userspace to turn this feature on/off >> Do the same for the receiver (useful for 2 wire RS485) > > I've been wondering about this as well but I have a slightly different > situation. On my board the RTS line controls the RS485 transmit/receive > direction. > > I don't know if you've found the Documentation/serial/serial-rs485.txt > file but it describes, at the very least, a standard API For controlling > several parameters related to RS485 including configurable delay between > rts->start of data/end of data->rts. Unfortunately it seems like only > one driver really implements the full API (Atmel AT91) and I guess it > needs to be bolted onto each serial driver individually (although it > seems like a fairly general concept that could be handled at another > level). > > That being said, maybe this patch would better be rethought as a way to > specify a GPIO for the RTS line (I don't know enough about OMAP and > whether or not it already provides for hardware flow control in its > builtin UARTs and you just aren't using it for RS485 flow control?) and > then in a separate patch implement this already documented user->kernel > API? I've actually submitted a newer version that does support the documented API. See http://permalink.gmane.org/gmane.linux.ports.arm.omap/102765 Does this address some of your questions ? -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
