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@linaro.org Signed-off-by: Anup Patel anup.patel@linaro.org --- 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));
/*