From: John Ogness Date: Wed, 6 May 2026 12:15:56 +0000 (+0206) Subject: serial: core: Add dedicated uart_port field for console flow X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9c7eb1c9c3e3bfecb556fc8fa1b68939385444de;p=thirdparty%2Fkernel%2Fstable.git 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 Link: https://patch.msgid.link/20260506121606.5805-2-john.ogness@linutronix.de Signed-off-by: Greg Kroah-Hartman --- diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index 666430b47899..4f7bbdd90017 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -533,6 +533,7 @@ struct uart_port { #define UPF_HARD_FLOW ((__force upf_t) (UPF_AUTO_CTS | UPF_AUTO_RTS)) /* Port has hardware-assisted s/w flow control */ #define UPF_SOFT_FLOW ((__force upf_t) BIT_ULL(22)) +/* Deprecated: use uart_set_cons_flow_enabled()/uart_cons_flow_enabled() instead. */ #define UPF_CONS_FLOW ((__force upf_t) BIT_ULL(23)) #define UPF_SHARE_IRQ ((__force upf_t) BIT_ULL(24)) #define UPF_EXAR_EFR ((__force upf_t) BIT_ULL(25)) @@ -567,6 +568,7 @@ struct uart_port { #define UPSTAT_SYNC_FIFO ((__force upstat_t) (1 << 5)) bool hw_stopped; /* sw-assisted CTS flow state */ + bool cons_flow; /* user specified console flow control */ unsigned int mctrl; /* current modem ctrl settings */ unsigned int frame_time; /* frame timing in ns */ unsigned int type; /* port type */ @@ -1163,6 +1165,16 @@ static inline bool uart_softcts_mode(struct uart_port *uport) return ((uport->status & mask) == UPSTAT_CTS_ENABLE); } +static inline void uart_set_cons_flow_enabled(struct uart_port *uport, bool enabled) +{ + uport->cons_flow = enabled; +} + +static inline bool uart_cons_flow_enabled(const struct uart_port *uport) +{ + return uport->cons_flow; +} + /* * The following are helper functions for the low level drivers. */