Messages in this thread | | | From | "Karicheri, Muralidharan" <> | Subject | RE: [PATCH] serial: uart: add hw flow control support configuration | Date | Wed, 23 Apr 2014 14:21:03 +0000 |
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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: devicetree@vger.kernel.org; linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org; >linux-serial@vger.kernel.org >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 <robh+dt@kernel.org> >CC: Pawel Moll <pawel.moll@arm.com> >CC: Mark Rutland <mark.rutland@arm.com> >CC: Ian Campbell <ijc+devicetree@hellion.org.uk> >CC: Kumar Gala <galak@codeaurora.org> >CC: Randy Dunlap <rdunlap@infradead.org> >CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >CC: Jiri Slaby <jslaby@suse.cz> > >Signed-off-by: Murali Karicheri <m-karicheri2@ti.com> >--- > .../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
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