linux-kernel - [RFC 2/2] virtio_console: Add feature to disable console port

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Date:	Mon,  3 Sep 2012 15:51:17 +0200
From:	sjur.brandeland@...ricsson.com
To:	Amit Shah <amit.shah@...hat.com>
Cc:	Sjur Brændeland <sjurbren@...il.com>,
	linux-kernel@...r.kernel.org,
	Sjur Brændeland <sjur.brandeland@...ricsson.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: [RFC 2/2] virtio_console: Add feature to disable console port

From: Sjur Brændeland <sjur.brandeland@...ricsson.com>

Add the feature VIRTIO_CONSOLE_F_NO_HVC. With this bit set
only port-devices are created. The console port and
port control virtio-queues are not created.

The console port is not suited for communicating
to a remote processor because of it's blocking behavior.
But the port-device supports efficient non-blocking IO
to a remote processor.

Signed-off-by: Sjur Brændeland <sjur.brandeland@...ricsson.com>
cc: Rusty Russell <rusty@...tcorp.com.au>
cc: Michael S. Tsirkin <mst@...hat.com>
cc: virtualization@...ts.linux-foundation.org
cc: Ohad Ben-Cohen <ohad@...ery.com>
cc: Linus Walleij <linus.walleij@...aro.org>
---
 drivers/char/virtio_console.c  |    5 ++++-
 include/linux/virtio_console.h |    1 +
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 6bfbd09..81546e9 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1246,7 +1246,9 @@ static int add_port(struct ports_device *portdev, u32 id)
 	/*
 	 * If we're not using multiport support, this has to be a console port
 	 */
-	if (!use_multiport(port->portdev)) {
+	if (virtio_has_feature(port->portdev->vdev, VIRTIO_CONSOLE_F_NO_HVC))
+		port->host_connected = true;
+	else if (!use_multiport(port->portdev)) {
 		err = init_port_console(port);
 		if (err)
 			goto free_inbufs;
@@ -1882,6 +1884,7 @@ static unsigned int features[] = {
 	VIRTIO_CONSOLE_F_SIZE,
 	VIRTIO_CONSOLE_F_MULTIPORT,
 	VIRTIO_CONSOLE_F_DMA_MEM,
+	VIRTIO_CONSOLE_F_NO_HVC,
 };
 
 #ifdef CONFIG_PM
diff --git a/include/linux/virtio_console.h b/include/linux/virtio_console.h
index b27f7fa..a7c8974 100644
--- a/include/linux/virtio_console.h
+++ b/include/linux/virtio_console.h
@@ -39,6 +39,7 @@
 #define VIRTIO_CONSOLE_F_SIZE	0	/* Does host provide console size? */
 #define VIRTIO_CONSOLE_F_MULTIPORT 1	/* Does host provide multiple ports? */
 #define VIRTIO_CONSOLE_F_DMA_MEM 2	/* Use DMA memory in vrings */
+#define VIRTIO_CONSOLE_F_NO_HVC 3	/* Disable use of HVC */
 
 #define VIRTIO_CONSOLE_BAD_ID		(~(u32)0)
 
-- 
1.7.5.4

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