Alan, Sorry, I had to cut-n-paste your comment as I lost your email from my inbox.
>-----Original Message----- >From: Karicheri, Muralidharan >Sent: Friday, April 11, 2014 3:18 PM >To: [email protected]; [email protected]; >[email protected]; >[email protected] >Cc: Balbi, Felipe; Karicheri, Muralidharan; Rob Herring; Mark Rutland; Ian >Campbell; >Kumar Gala; Randy Dunlap; Greg Kroah-Hartman; Jiri Slaby >Subject: [PATCH] serial: uart: add hw flow control support configuration > >8250 uart driver currently supports only software assisted hw flow control. >The software >assisted hw flow control maintains a hw_stopped flag in the tty structure to >stop and start >transmission and use modem status interrupt for the event to drive the >handshake signals. >This is not needed if hw has flow control capabilities. This patch adds a DT >attribute for >enabling hw flow control for a uart port. Also skip stop and start if this >flag is present in flag >field of the port structure. [Alan] That seems a sensible thing to add. > >CC: Rob Herring <[email protected]> >CC: Pawel Moll <[email protected]> >CC: Mark Rutland <[email protected]> >CC: Ian Campbell <[email protected]> >CC: Kumar Gala <[email protected]> >CC: Randy Dunlap <[email protected]> >CC: Greg Kroah-Hartman <[email protected]> >CC: Jiri Slaby <[email protected]> > >Signed-off-by: Murali Karicheri <[email protected]> >--- > .../devicetree/bindings/serial/of-serial.txt | 2 ++ > drivers/tty/serial/8250/8250_core.c | 6 ++++-- > drivers/tty/serial/of_serial.c | 4 ++++ > drivers/tty/serial/serial_core.c | 12 +++++++++--- > 4 files changed, 19 insertions(+), 5 deletions(-) > >diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt >b/Documentation/devicetree/bindings/serial/of-serial.txt >index 1928a3e..123de01 100644 >--- a/Documentation/devicetree/bindings/serial/of-serial.txt >+++ b/Documentation/devicetree/bindings/serial/of-serial.txt >@@ -37,6 +37,8 @@ Optional properties: > - auto-flow-control: one way to enable automatic flow control support. The > driver is allowed to detect support for the capability even without this > property. >+- hw-flow-control: this enables pure hw flow control and no software >+ intervention needed. > > Example: > >diff --git a/drivers/tty/serial/8250/8250_core.c >b/drivers/tty/serial/8250/8250_core.c >index 81f909c..6b1b868 100644 >--- a/drivers/tty/serial/8250/8250_core.c >+++ b/drivers/tty/serial/8250/8250_core.c >@@ -2338,9 +2338,11 @@ serial8250_do_set_termios(struct uart_port *port, struct >ktermios *termios, > * the trigger, or the MCR RTS bit is cleared. In the case where > * the remote UART is not using CTS auto flow control, we must > * have sufficient FIFO entries for the latency of the remote >- * UART to respond. IOW, at least 32 bytes of FIFO. >+ * UART to respond. IOW, at least 32 bytes of FIFO. Also enable >+ * AFE if hw flow control is supported > */ >- if (up->capabilities & UART_CAP_AFE && port->fifosize >= 32) { >+ if ((up->capabilities & UART_CAP_AFE && (port->fifosize >= 32)) || >+ port->flags & UPF_HARD_FLOW) { [Alan] Surely you want brackets on the port->flags & UPF_HARD_FLOW ?? The C precedence table shows following order:= -> & || So flags will be accessed first and then AND-ed with UPF_HARD_FLOW and result will be OR-ed with left side expression value. So no need for bracket IMO. Murali -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
