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

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Date:	Mon, 13 May 2013 12:26:39 +0530
From:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	Anup Patel <anup.patel@...aro.org>,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH V2 2/3] Documentation: virtio: Add emergency write
 (emerg_wr) config register in virtio console.

Hi Rusty,

On 13 May 2013 08:22, Rusty Russell <rusty@...tcorp.com.au> wrote:
> 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 for applying this patch.
Have you also applied first patch ([PATCH V2 1/3] virtio: console: Add
emergency writeonly register to config space)
with this?  (https://lkml.org/lkml/2013/5/6/169)

>
> Thanks,
> Rusty.

Thanks,
Pranav

>
>> 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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