[Intel-gfx] [PATCH 1/2] drm/i915: Detect SDVO-RGB before SDVO TV

[Fu Michael]

Eric Anholt wrote:
> On Wed, 27 Jan 2010 16:32:45 +0800, yakui.zhao at intel.com wrote:
>   
>> From: Zhao Yakui <yakui.zhao at intel.com>
>>
>> Some VGA/TV dual function SDVO card  with only VGA port incorrectly report all
>> kinds of its connection as connected when VGA monitor is connected.
>> This patch workaround it.
>>
>> http://bugs.freedesktop.org/show_bug.cgi?id=25787
>>
>> Signed-off-by: Zhao Yakui <yakui.zhao at intel.com>
>>     
>
> Why should what order the connectors get set up matter?  If it's supposed
> to matter, has this been tested in anything other than this guy's
> particular configuration to make sure that you're not regressing other
> picky encoders?
>
> If I had to take a wild guess, this would be another manifestation of
> the failure of the SDVO code to have a single encoder instance managing
> the multiple connectors attached to it, so the different connectors
> fight over the state of the encoder.
>   
actually it's not the code but the card in this case.

we have only one way to know what kind of monitor is attached to a sDVO 
card, that is to send a command to it and read back response. For the 
card in this bug report, even though it only has VGA attached. It report 
all of its capabilities are connected, which apparently is not true. if 
we just pass that message up to user space, the bogus connection would 
mess up mode setting then, so technically, this is a patch in UMS that 
happen worked around it.

Such kind of multi-function sdvo card is rare. we don't have any, and we 
only see one bug report from community in our bugzilla as well.  I guess 
that's why UMS has been living with it fine for a long time.

 I guess if we want a decent fix for this, maybe our last hope is to see 
if VBT has any information to tell us not to bother with other type but 
just one kind of connector on this SDVO device. But I'm not sure if this 
would break other normal cards then, just in case a VBT is broken...
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