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

Grant Edwards
2008-08-07T13:50:38Z

On 2008-08-07, Laurent Pinchart <laurentp@cse-semaphore.com> wrote:

>> 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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