Re: [Qemu-devel] [PATCH] Realview/Versatile: Export LED state

[Wolfgang Mauerer <wolfgang.mauerer@siemens.com>]

On 11/01/13 16:23, Andreas Färber wrote:
> Am 11.01.2013 16:00, schrieb Peter Maydell:
>> On 11 January 2013 13:42, Wolfgang Mauerer <wolfgang.mauerer@siemens.com> wrote:
>>> The configuration register for the onboard LEDs is
>>> emulated, but the state is not exported, which makes
>>> the feature not particularly useful. Create a character
>>> device to make status changes accessible to the host.
>>>
>>> For example, use the command line argument
>>>
>>> -chardev socket,id=leds,host=localhost,port=12345,server,nowait
>>>
>>> to observe status changes via a socket.
>>
>> This isn't the only board we emulate which has LEDs. I'd
>> rather see this problem tackled with a general plan for "this
>> is how we handle LEDs in QEMU boards" rather than a
>> versatile board specific patch.
> 
> Hm, mips_malta.c does use a CharDriverState... just a more "structured"
> one using ASCII art.

that's one of the reaons why I used a character device to export the
status information.

However, a simple custom protocol (or maybe the same information in
JSON) seemed more appripriate since I assume that graphical frontends
will eventually visualise the LED status. Having to parse some ASCII
art output for this seems suboptimal.

Exporting a binary QOM property (as you suggested in another email)
might be an option, although I'm not really sure if LED status changes
should be communicated this way -- to me, using a chardev feels nicer.
Do the QMP maintainers have an opinion?

Regards, Wolfgang