[PATCH 3/5] serial: virtio_console: report the console size

[Ahmad Fatoum <a.fatoum@barebox.org>]

Hosts that offer VIRTIO_CONSOLE_F_SIZE, like TinyEMU, keep the size of
their terminal in the config space. Implement get_size with it, so that
sedit and watch don't need to query the terminal and wait up to 100ms
for the reply. When the reply takes longer, as in the barebox web demo,
sedit gives up and the reply ends up in the edited file:

  [24;80R#!/bin/sh

Signed-off-by: Ahmad Fatoum <a.fatoum@barebox.org>
---
 drivers/serial/virtio_console.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/serial/virtio_console.c b/drivers/serial/virtio_console.c
index ae36cad6e5bd..3d14bf502489 100644
--- a/drivers/serial/virtio_console.c
+++ b/drivers/serial/virtio_console.c
@@ -18,6 +18,7 @@
 #include <xfuncs.h>
 #include <linux/spinlock.h>
 #include <linux/virtio.h>
+#include <linux/virtio_config.h>
 #include <linux/virtio_ring.h>
 #include <linux/virtio_console.h>
 
@@ -105,6 +106,24 @@ static int virtcons_getc(struct console_device *cdev)
 	return ch;
 }
 
+static int virtcons_get_size(struct console_device *cdev, int *width, int *height)
+{
+	struct virtio_device *vdev = dev_to_virtio(cdev->dev);
+	u16 cols, rows;
+
+	virtio_cread(vdev, struct virtio_console_config, cols, &cols);
+	virtio_cread(vdev, struct virtio_console_config, rows, &rows);
+
+	/* the host may not have filled them in yet */
+	if (!cols || !rows)
+		return -ENODATA;
+
+	*width = cols;
+	*height = rows;
+
+	return 0;
+}
+
 static int virtcons_probe(struct virtio_device *vdev)
 {
 	struct virtqueue *vqs[2];
@@ -146,6 +165,8 @@ static int virtcons_probe(struct virtio_device *vdev)
 	virtcons->cdev.tstc = virtcons_tstc;
 	virtcons->cdev.getc = virtcons_getc;
 	virtcons->cdev.putc = virtcons_putc;
+	if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
+		virtcons->cdev.get_size = virtcons_get_size;
 
 	have_one = true;
 
@@ -168,9 +189,15 @@ static struct virtio_device_id id_table[] = {
 	{ 0 },
 };
 
+static const unsigned int features[] = {
+	VIRTIO_CONSOLE_F_SIZE,
+};
+
 static struct virtio_driver virtio_console = {
 	.driver.name =	"virtio_console",
 	.id_table =	id_table,
+	.feature_table = features,
+	.feature_table_size = ARRAY_SIZE(features),
 	.probe =	virtcons_probe,
 	.remove =	virtcons_remove,
 };
-- 
2.47.3