Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | Re: [PATCH 0/2] Early printk support for virtio console devices. | Date | Mon, 06 May 2013 14:41:46 +0930 |
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Peter Maydell <peter.maydell@linaro.org> writes: > On 1 May 2013 03:07, Rusty Russell <rusty@rustcorp.com.au> wrote: >> An emergency output is a reasonable idea, and this is a reasonable >> implementation. The question is practical: will it be used? Because we >> don't implement reasonable ideas which aren't going to be used. > > If you think it fits reasonably into the virtio spec (ie doesn't > implement things at the wrong level of the transport/backend > abstraction) then we can implement it in QEMU, and I think it > makes more sense to do this than to throw in a random extra > serial port. > > To be actually useful we need to also specify something in > the device tree to say "here is where you will find your > emergency output and what it is".
Hmm, I'm not sure that's true. It looks like it needs:
1) An enhancment to the vdev->set_config callback to pass through (at least) an offset, probably offset and length.
2) An emerg_write() function ptr which can be called at any time, set by virtio_console.c's class_init:
static void emerg_write(VirtIOSerialPort *port, char c) { VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
if (vcon->chr) qemu_chr_fe_write(vcon->chr, &c, 1); }
3) A routine to find an emerg-write-capable console in virtio_serial_bus.c (or just assume port 0?):
static VirtIOSerialPort *find_emerg_write_port(VirtIOSerial *vser) { VirtIOSerialPort *port;
QTAILQ_FOREACH(port, &vser->ports, next) { VirtIOSerialPortClass *vsc; vsc = VIRTIO_SERIAL_PORT_GET_CLASS(port);
if (vsc->emerg_write) { return port; } } return NULL; }
4) set_config in virtio_serial_bus.c to notice emergency writes:
if (offset == offsetof(struct virtio_console_config, emerg_w) { VirtIOSerial *vser; vser = DO_UPCAST(VirtIOSerial, vdev, vdev); VirtIOSerialPort *port;
port = find_emerg_write_port(vser); if (port) { vsc->emerg_write(port, config.emerg_w); } }
Amit might have more clue... Amit?
Thanks, Rusty.
From: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> Subject: virtio: console: Add early writeonly register to config space
This patch adds a emerg_wr register (writeonly) in config space of virtio console device which can be used for debugging.
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> Signed-off-by: Anup Patel <anup.patel@linaro.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> --- include/uapi/linux/virtio_console.h | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/include/uapi/linux/virtio_console.h b/include/uapi/linux/virtio_console.h index ee13ab6..586678d 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_EMERG_WRITE 2 /* Does host support emergency 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; + /* emergency write register */ + __u32 emerg_wr; } __attribute__((packed)); /*
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