linux-kernel - Re: [PATCH v3] fbcon: add fbcon=margin:<color> command line option

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Date:   Fri, 18 Aug 2017 14:19:28 -0500
From:   David Lechner <david@...hnology.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] fbcon: add fbcon=margin:<color> command line option

On 08/18/2017 01:21 PM, Geert Uytterhoeven wrote:
> Hi David,
> 
> On Tue, Aug 1, 2017 at 6:35 PM, David Lechner <david@...hnology.com> wrote:
>> This adds a new command line option to select the fbcon margin color.
>>
>> The motivation for this is screens where black does not blend into the
>> physical surroundings of the screen. For example, using an LCD (not the
>> backlit kind), white text on a black background is hard to read, so
>> inverting the colors is preferred. However, when you do this, most of the
>> screen is filled with white but the margins are still filled with black.
>> This makes a big, black, backwards 'L' on the screen. By setting
>> fbcon=margin:7, the margins will be filled with white and the LCD looks as
>> expected.
>>
>> Signed-off-by: David Lechner <david@...hnology.com>
> 
>> --- a/Documentation/fb/fbcon.txt
>> +++ b/Documentation/fb/fbcon.txt
>> @@ -148,6 +148,13 @@ C. Boot options
>>          Actually, the underlying fb driver is totally ignorant of console
>>          rotation.
>>
>> +5. fbcon=margin:<color>
>> +
>> +       This option specifies the color of the margins. The margins are the
>> +       leftover area at the right and the bottom of the screen that are not
>> +       used by text. By default, this area will be black. The 'color' value
>> +       is 0 to 7 where 0 is black and 7 is white.
>> +
> 
> Given the standard console palette contains 16 colors, why limit this to
> the first 8 colors, and not 0 to 15?

Good question. I think in some of my previous attempts there was a 0x7 
mask involved somewhere and this is a carryover from that. But, after 
having looked at this again, I don't see a reason for limiting to 7.