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

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Message-ID: <CAKMK7uFotPC98xEYUQJ2O7m=PtWqurku1HqFpEzwzppJZD=5tQ@mail.gmail.com>
Date:   Thu, 3 Aug 2017 01:28:27 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     David Lechner <david@...hnology.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH] drm/fb-helper: pass physical dimensions to fbdev

On Wed, Aug 2, 2017 at 6:37 PM, David Lechner <david@...hnology.com> wrote:
> On 08/02/2017 04:46 AM, Daniel Vetter wrote:
>>
>> On Tue, Aug 01, 2017 at 10:26:41AM -0500, 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.
>>>
>>> Signed-off-by: David Lechner <david@...hnology.com>
>>
>>
>> Still in the wrong function. Also please add some notation about what you
>> changed when resubmitting a patch (it took me a while to remember that I
>> replied to you already). That makes patch reviewing more efficient.
>>
>
> Sorry for being so dense. :-/
>
> I did read your first reply at least 10 times. All of the terminology is
> foreign to me, but after sleeping on it a few days, I think it is slowly
> soaking into my brain.

No problem, the code is fairly convoluted. One more question on your
v3: From reading fbdev code I don't see any place that overwrites the
physical dimensions except the fill_var helper function (which is
called deep down from register_framebuffer). If we entirely remove the
var.width/height assignments from that (including the -1 default) and
move all of it into setup_crtcs, would that work?

I kinda don't like have the same logic in 2 completely different
places, once for driver load and once for hotplug handling. That tends
to cause bugs (because then no one bothers to test hotplug handling or
the boot-up case properly).

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch