linux-kernel - Re: KMS question

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Date:   Thu, 13 Apr 2017 11:36:45 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Boszormenyi Zoltan <zboszor@...hu>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>
Subject: Re: KMS question

On Thu, Apr 13, 2017 at 11:03 AM, Boszormenyi Zoltan <zboszor@...hu> wrote:
> 2017-04-13 16:05 keltezéssel, Alex Deucher írta:
>>
>> On Thu, Apr 13, 2017 at 9:03 AM, Boszormenyi Zoltan <zboszor@...hu> 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:
>> https://wiki.archlinux.org/index.php/kernel_mode_setting
>> 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?

Alex