This patch adds a early_wr register (writeonly) in config space of virtio console device which can be used for debugging.
The patch also updates virtio-spec in Documentation to reflect this feature addition in virtio console.
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>
Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxx>
---
Documentation/virtual/virtio-spec.txt | 13 +++++++++++--
include/uapi/linux/virtio_console.h | 3 +++
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt
index 0d6ec85..bc4e8b5 100644
--- a/Documentation/virtual/virtio-spec.txt
+++ b/Documentation/virtual/virtio-spec.txt
@@ -1927,11 +1927,18 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set
ports; configuration fields nr_ports and max_nr_ports are
valid and control virtqueues will be used.
+ VIRTIO_CONSOLE_F_EARLY_WRITE(2) Device has support for early
+ write. Configuration field early_wr is valid.
+
Device configuration layout The size of the console is supplied
in the configuration space if the VIRTIO_CONSOLE_F_SIZE feature
is set. Furthermore, if the VIRTIO_CONSOLE_F_MULTIPORT feature
is set, the maximum number of ports supported by the device can
- be fetched.struct virtio_console_config {
+ be fetched. If VIRTIO_CONSOLE_F_EARLY_WRITE is set then one can
+ use early write to output single character without initializing
+ virtio queues.
+
+ struct virtio_console_config {
u16 cols;
@@ -1941,7 +1948,9 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set
u32 max_nr_ports;
-};
+ u32 early_wr;
+
+ };
Device Initialization
diff --git a/include/uapi/linux/virtio_console.h b/include/uapi/linux/virtio_console.h
index ee13ab6..7cd84b5 100644
--- a/include/uapi/linux/virtio_console.h
+++ b/include/uapi/linux/virtio_console.h
@@ -38,6 +38,7 @@
/* Feature bits */
#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_EARLY_WRITE 2 /* Does host support early write? */
#define VIRTIO_CONSOLE_BAD_ID (~(u32)0)
@@ -48,6 +49,8 @@ struct virtio_console_config {
__u16 rows;
/* max. number of ports this device can hold */
__u32 max_nr_ports;
+ /* early write register */
+ __u32 early_wr;
} __attribute__((packed));
/*
--
1.7.9.5
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