serial: core: Add dedicated uart_port field for console flow

Currently the UPF_CONS_FLOW bit in the uart_port.flags field is used
by serial console drivers to identify if a user has configured flow
control on the console. Usually this policy is setup during early
boot, but can be changed at runtime.

The bits in uart_port.flags are either hardware and driver
properties that are initialized before usage or are properties that
can be changed via the tty layer.

The UPF_CONS_FLOW bit is an exception because it is a console-only
policy that can change at runtime and its setting and usage have
nothing to do with the tty layer. This actually causes a problem
for its usage because uart_port.flags is synchronized by a related
tty_port.mutex, but a console has no relation to a tty (other than
sharing the port).

This is probably why console flow control is not properly available
for most serial drivers. And it is hindering being able to provide a
proper implementation. Commit d01f4d181c92 ("serial: core: Privatize
tty->hw_stopped") addressed a similar issue to deal with software
assisted CTS flow state tracking.

Add a new uart_port boolean field "cons_flow" to store the user
configuration for console flow control. Add getter/setter wrappers
to allow for adding more policies later and/or locking constraint
validation.

Mark UPF_CONS_FLOW as deprecated.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20260506121606.5805-2-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions