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Date:   Thu, 13 Apr 2017 11:37:45 -0400
From:   Ilia Mirkin <imirkin@...m.mit.edu>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     Boszormenyi Zoltan <zboszor@...hu>,
        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 11:36 AM, Alex Deucher <alexdeucher@...il.com> wrote:
> 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?

I think the video= based disable forces the connector to be disabled
irrevocably.

  -ilia

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