diff mbox series

[v3,1/2] serial: 8250: Add flag so drivers can avoid THRE probe

Message ID 20170410035904.29443-2-joel@jms.id.au
State Accepted
Commit ea5244e2af3b4813bf3d90ba6a6481d1a3c33d15
Headers show
Series [v3,1/2] serial: 8250: Add flag so drivers can avoid THRE probe | expand

Commit Message

Joel Stanley April 10, 2017, 3:59 a.m. UTC 
The probing of THRE irq behaviour assumes the other end will be reading
bytes out of the buffer in order to probe the port at driver init. In
some cases the other end cannot be relied upon to read these bytes, so
provide a flag for them to skip this step.

Bit 19 was chosen as the flags are a int and the top bits are taken.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Signed-off-by: Joel Stanley <joel@jms.id.au>


---
v3:
 - Correct the bit number in the changelog

v2:
 - No change

 drivers/tty/serial/8250/8250_port.c | 2 +-
 include/linux/serial_core.h         | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

-- 
2.11.0

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diff mbox series

Patch

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 6119516ef5fc..60a6c247340f 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2229,7 +2229,7 @@  int serial8250_do_startup(struct uart_port *port)
 		}
 	}
 
-	if (port->irq) {
+	if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
 		unsigned char iir1;
 		/*
 		 * Test for UARTs that do not reassert THRE when the
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 58484fb35cc8..260245deec94 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -195,6 +195,7 @@  struct uart_port {
 #define UPF_NO_TXEN_TEST	((__force upf_t) (1 << 15))
 #define UPF_MAGIC_MULTIPLIER	((__force upf_t) ASYNC_MAGIC_MULTIPLIER /* 16 */ )
 
+#define UPF_NO_THRE_TEST	((__force upf_t) (1 << 19))
 /* Port has hardware-assisted h/w flow control */
 #define UPF_AUTO_CTS		((__force upf_t) (1 << 20))
 #define UPF_AUTO_RTS		((__force upf_t) (1 << 21))