KMS question

Boszormenyi Zoltan zboszor at
Thu Apr 13 15:48:45 UTC 2017

2017-04-13 17:36 keltezéssel, Alex Deucher írta:
> On Thu, Apr 13, 2017 at 11:03 AM, Boszormenyi Zoltan <zboszor at> wrote:
>> 2017-04-13 16:05 keltezéssel, Alex Deucher írta:
>>> On Thu, Apr 13, 2017 at 9:03 AM, Boszormenyi Zoltan <zboszor at> 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?

No, "xrandr --output DVI-D-1 --auto" does nothing.

> Alex

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