linux-kernel - Re: [PATCH v5] drm/fb-helper: pass physical dimensions to fbdev

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Message-ID: <3ac80a0e-707c-6bf9-4e19-d3a455303ff4@lechnology.com>
Date:   Sat, 5 Aug 2017 10:57:50 -0500
From:   David Lechner <david@...hnology.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH v5] drm/fb-helper: pass physical dimensions to fbdev

On 08/04/2017 04:53 PM, Laurent Pinchart wrote:
> Hi David,
> 
> Thank you for the patch.
> 
> On Friday 04 Aug 2017 11:25:24 David Lechner wrote:
>> The fbdev subsystem has a place for physical dimensions (width and height
>> in mm) that is readable by userspace. Since DRM also knows these
>> dimensions, pass this information to the fbdev device.
> 
> I'm curious, what's your use case for this ? What userspace software do you
> use that is still based on fbdev and needs screen dimensions ?


I have dug up an old graphics library called GRX[1] and modernized 
it[2]. So, I am using the screen dimensions to make it DPI-aware so that 
the font on my 2.4" screen looks the same size as my 2.8" screen when 
both are 320x240 pixels. Until this year, all of the displays I have 
only have fbdev drivers.

[1]: http://grx.gnu.de
[2]: https://github.com/ev3dev/grx