[v2,1/2] serial: 8250: Add flag so drivers can avoid THRE probe

Submitted by Joel Stanley on April 5, 2017, 4:03 a.m.

Details

Message ID 20170405040352.5661-2-joel@jms.id.au
State New
Headers show

Commit Message

Joel Stanley April 5, 2017, 4:03 a.m.
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 16 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>
---
 drivers/tty/serial/8250/8250_port.c | 2 +-
 include/linux/serial_core.h         | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

Comments

Andy Shevchenko April 5, 2017, 10:36 a.m.
On Wed, Apr 5, 2017 at 7:03 AM, Joel Stanley <joel@jms.id.au> wrote:
> 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 16 was chosen as the flags are a int and the top bits are taken.

19 ?

>
> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
>  drivers/tty/serial/8250/8250_port.c | 2 +-
>  include/linux/serial_core.h         | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> 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))
> --
> 2.11.0
>

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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))