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Date:   Thu, 13 Apr 2017 19:32:56 +0200
From:   Boszormenyi Zoltan <>
To:     Ville Syrjälä <>,
        Ilia Mirkin <>
Cc:     lkml <>,
        Maling list - DRI developers 
Subject: Re: KMS question

2017-04-13 18:20 keltezéssel, Ville Syrjälä írta:
> On Thu, Apr 13, 2017 at 11:37:45AM -0400, Ilia Mirkin wrote:
>> On Thu, Apr 13, 2017 at 11:36 AM, Alex Deucher <> wrote:
>>> On Thu, Apr 13, 2017 at 11:03 AM, Boszormenyi Zoltan <> wrote:
>>>> 2017-04-13 16:05 keltezéssel, Alex Deucher írta:
>>>>> On Thu, Apr 13, 2017 at 9:03 AM, Boszormenyi Zoltan <> wrote:
>>>>>> Hi,
>>>>>> how can I disable the behaviour in the KMS drivers
>>>>>> that enables all outputs at once?
>>>>>> It is very annoying that on a POS machine with an
>>>>>> 1024x768 LVDS and a 800x480 secondary monitor (both built-in)
>>>>>> the KMS driver wakes up both. Then the framebuffer console
>>>>>> and plymouth use both screens, making the primary output
>>>>>> very odd with only the top-left part used by the boot splash.
>>>>>> I would like the boot splash to be shown only on the primary
>>>>>> output at its full resolution instead of on all outputs using
>>>>>> the smallest common rectangle.
>>>>>> Is there a kernel command line configuration that achieves this?
>>>>>> The device in question uses the gma500 kernel driver but the same
>>>>>> behaviour is observed with the i915 and radeon drivers.
>>>>> The problem is fbdev is not multi-head aware.  The fbdev emulation in
>>>>> the KMS drivers attempts to light up all monitors so that something
>>>>> shows up on all heads.  If you really want different per head
>>>>> configurations, you need to use the KMS API directly.  As a
>>>>> workaround, you can use the kernel command line to disable the output
>>>>> you don't want to be lit up.  See:
>>>>> for more info.  basically add video=TV-1:d to disable the output in
>>>>> question.  Replace TV-1 with whatever connector you want to disable.
>>>> I tried adding video=DVI-D-1:d to the kernel command line.
>>>> The effect is while the second output is indeed disabled, the
>>>> framebuffer console still takes the second output's resolution
>>>> into account and the boot splash is still using only the top-left
>>>> 800x480 part of the 1024x768 primary screen.
>>>> Also, the secondary screen got disabled also in X which is not desired.
>>>> Can I wake it up under X somehow? This device is using the modesetting
>>>> DDX driver.
>>> Can you enable it via randr?
>> I think the video= based disable forces the connector to be disabled
>> irrevocably.
> # echo detect > /sys/class/drm/<whatever>/status

Thanks, that worked.

I had to regenerate my initramfs to actually include the gma500 driver
so KMS can kick in early. Before that the text mode plugin was used in
plymouth and that doesn't switch dimensions when fbdev took over.

The plymouth boot splash now looks good on the primary screen with
the secondary display disabled from the kernel command line and I can
enable the secondary screen from a boot script before X (a DM) starts
which causes both screens to flash but it's good for me now.

Thanks for everyone who answered.

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