Re: [PATCH/RFC] 8250: Auto RS485 direction control

On 2008-08-07, Laurent Pinchart [off-list ref] wrote:

quoted

From what I can gather through the man pages it seems inappropriate to
add this to termios cflag, though the CRTSCTS flag does set a precedent.
I'm an advocate of the idea of introducing a new IOCTL for setting up
non standard hand-shaking settings.  I would suggest that things that
should be considered in the interface are settings for lead-in and
lead-out timing on the direction line (for the use of radio modems for
example) and means to specify if it's appropriate to have the CPU spin
on the shift register empty flag on the last byte of a block, if RTS
timing really is that critical.

I don't think we want to introduce software emulation, but
feel free to prove me wrong.

I think that should be left up to the author of the driver.  It
seems to me that it would be pretty difficult to do a decent
job of it at the line-discipline layer.  If the author of the
driver for a particular UART wants to do SW emulation of
auto-RTS, then I think that's where it belongs.  Only the UART
driver knows whether there's a shift-register empty interrupt
(and whether that interrupt happens before or after that final
stop bit has been transmitted).

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