gtk+ and randr

[Maarten Maathuis]

On Tue, Jul 22, 2008 at 11:24 PM, Dave Airlie <airlied at gmail.com> wrote:
> On Wed, Jul 23, 2008 at 7:19 AM, Maarten Maathuis <madman2003 at gmail.com> wrote:
>> On Tue, Jul 22, 2008 at 11:04 PM, Dave Airlie <airlied at gmail.com> wrote:
>>> On Wed, Jul 23, 2008 at 3:19 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
>>>> On Tue, Jul 22, 2008 at 12:38 PM, Eric Piel <E.A.B.Piel at tudelft.nl> wrote:
>>>>> Alex Deucher schreef:
>>>>>>
>>>>>> On Tue, Jul 22, 2008 at 4:18 AM, Eric Piel <E.A.B.Piel at tudelft.nl> wrote:
>>>>>>>
>>>>>>> Alex Deucher schreef:
>>>>>>>>
>>>>>>>> On Mon, Jul 21, 2008 at 6:39 PM, Ben Gamari <ben at mw0.ath.cx> wrote:
>>>>>>>>>
>>>>>>>>> On Intel hardware it seems to probe the outputs and re-acquire EDID
>>>>>>>>> information, which in itself seems to usually cause loss of sync. It
>>>>>>>>> seems this is what XRRGetScreenResources() is supposed to do so I
>>>>>>>>> really
>>>>>>>>> don't see any way to avoid the cost.
>>>>>>>>
>>>>>>>> If you have monitors with EDIDs plugged into your connectors, then
>>>>>>>> you're fine.  if you have nothing on one or more connectors or a
>>>>>>>> monitor without an EDID, you may get flickering as the driver attempts
>>>>>>>> to use load detection to sense the presence of a monitor since there
>>>>>>>> is no EDID.
>>>>>>>
>>>>>>> With my i965 and a monitor _with_ EDID connected to the VGA output, I do
>>>>>>> get
>>>>>>> flickering (the screen turns black for one second). So, it seems the
>>>>>>> flickering happens all the time. Is it a bug in the intel driver? Or
>>>>>>> maybe
>>>>>>> it's because there is also a TV output? (that would be nasty because the
>>>>>>> laptop don't even have the plug!)
>>>>>>
>>>>>> TV is load detection only, so it's probably the tv port.  I suspect
>>>>>> your laptop needs a quirk to ignore the tv connector.
>>>>>
>>>>> Oh well, I've doubled checked, and if you buy the "media station" for my
>>>>> laptop, the tv connector is available. So it's better not to disable it
>>>>> completely!
>>>>>
>>>>> Still, isn't it strange that the fact there is a "load detection" on the TV
>>>>> output affects the VGA output?
>>>>
>>>> No, load detection requires a crtc as you need to send a signal to the
>>>> tv dac to check the load.  So what happens is the crtc that's
>>>> currently driving one of the other outputs is borrowed temporarily to
>>>> do the load detection, hence the flicker.
>>>>
>>>
>>> I've been thinking about this and I think we should change the
>>> detection ordering.
>>>
>>> Instead of just going through the outputs one by one we should go
>>> through the outputs that
>>> were connected the last time we checked first. So if for example on
>>> radeon we have a shared DAC,
>>> we can see the VGA is still connected to it, and not bother with TV
>>> load detection. This should remove
>>> some of the flickering cases we see today on radeon.. On intel if we
>>> can't get a crtc we shouldn't bother load detecting
>>> instead of stealing a crtc from an active output.
>>
>> This is very device dependent, and randr-1.2 has "no idea" of all
>> this. For modesetting-101 a fill_all_modes function could do the trick
>> and something similar could also be done for randr-1.2. It all boils
>> down to handing more control to the driver. Maybe randr-1.3 could also
>> replace other functions with stuff a la set_mode_major.
>>
>
> With randr-1.2 my scheme would work fine, just do the detects in order
> of what was connected previously.
> Then if the VGA turns out to be now disconnected, then the TV detect
> can know it can use the DAC to detect.

But how do you know dac sharing occurs? How do you know you need a
crtc for load detect or not?

>
> Yes its not as clean as a handing all of it to the driver, but I can't
> see why it would make it worse..
>
> Dave.
>