Flow control settings for RS232 modems

[Dan Williams]

On Sat, 2017-03-25 at 19:32 +0100, Aleksander Morgado wrote:
> Hey Dan, Daniele, Carlo & everyone,
> 
> This series of patches tries to implement proper flow control
> settings on the serial port, and is based on letting MM detect which
> are the supported modes with AT+IFC=?. This makes it unnecessary to
> subclass the flow control setting in plugins for modems that don't
> support XON/XOFF (what was being used as default), like the Telit
> plugin.

In general, patches 1-7 look good to me.  Only one comment on patch 8.

Dan

> The new logic will:
>   * Always open the serial ports without any flow control enabled.
>   * Query the modem which flow control methods are supported, with
> AT+IFC=?.
>   * If supported, prefer RTS/CTS over XON/XOFF, and notify the modem
> via AT+IFC=x,x our selection.
>   * When the port gets connected after an ATD call, reconfigure the
> TTY with the flow control attributes corresponding to the method we
> selected via AT+IFC.
>   * pppd may be run without any of the explicit options regarding
> flow control, which means that whatever was configured in the TTY is
> used.
>   * On port disconnection, we clear the flow control attributes of
> the TTY explicitly, although this is really not totally needed as we
> fully close and re-open the port (and during the re-open the port is
> opened without flow control enabled).
> 
> I prepared this logic for the Telit LE866-SV1, although it really is
> generic for every RS232 modem out there.
> 
> What do you guys think?
> 
> [PATCH 1/8] helpers: new parser for AT+IFC=?
> [PATCH 2/8] broadband-modem: query supported flow control modes
> [PATCH 3/8] wavecom: ignore custom flow control handling
> [PATCH 4/8] telit: ignore custom flow control handling
> [PATCH 5/8] port-serial: new internal method to run tcsetattr()
> [PATCH 6/8] port-serial: new method to explicitly set flow control
> [PATCH 7/8] port-serial: remove all default flow control settings
> [PATCH 8/8] broadband-bearer: once connected, set flow control
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