linux-kernel - Re: [PATCH V2 2/3] Documentation: virtio: Add emergency write (emerg

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Date:	Mon, 13 May 2013 12:22:07 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Cc:	kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	anup.patel@...aro.org, amit.shah@...hat.com,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
Subject: Re: [PATCH V2 2/3] Documentation: virtio: Add emergency write (emerg_wr) config register in virtio console.

Pranavkumar Sawargaonkar <pranavkumar@...aro.org> writes:
> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
> Signed-off-by: Anup Patel <anup.patel@...aro.org>
> ---
>  Documentation/virtual/virtio-spec.txt |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

OK, I applied this to the lyx master, with three changes:
1) Changed "filed" to "field".
2) Added ", or even acknowledging the feature" after "without
   initializing virtio queues".
3) Added an initial point to the Device Initialization section:

   1. If the VIRTIO_CONSOLE_F_EMERG_WRITE feature is offered, the
   emerg_wr field of the configuration can be written at any time. Thus
   it should work for very early boot debugging output as well as
   catastophic OS failures (eg. virtio ring corruption).

Thanks,
Rusty.

> diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt
> index 0d6ec85..3ca38f8 100644
> --- a/Documentation/virtual/virtio-spec.txt
> +++ b/Documentation/virtual/virtio-spec.txt
> @@ -1927,11 +1927,16 @@ 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_EMERG_WRITE(2) Device has support for emergency
> +  write. Configuration filed emerg_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_EMERG_WRITE is set then one can
> +  use emergency write to output single character without initializing
> +  virtio queues. struct virtio_console_config {
>  
>  	u16 cols;
>  
> @@ -1941,6 +1946,7 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set
>  
>  	u32 max_nr_ports;
>  
> +	u32 emerg_wr;
>  };
>  
>    Device Initialization
> -- 
> 1.7.9.5
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