Re: [PATCH v2] drm: get fbdev size from cmdline mode if it exists

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: dri-devel@lists.freedesktop.org
Cc: Yannick FERTRE <yannick.fertre@st.com>,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Vincent ABRIOU <vincent.abriou@st.com>,
	Fabien DESSENNE <fabien.dessenne@st.com>
Subject: Re: [PATCH v2] drm: get fbdev size from cmdline mode if it exists
Date: Tue, 10 Jan 2017 22:06:44 +0200	[thread overview]
Message-ID: <3414908.CWO1Stb0eH@avalon> (raw)
In-Reply-To: <fb61890c-e139-237e-4b30-602fc24df119@st.com>

Hi Vincent,

On Tuesday 10 Jan 2017 13:33:29 Vincent ABRIOU wrote:
> On 01/10/2017 12:39 PM, Daniel Vetter wrote:
> > On Tue, Jan 10, 2017 at 12:21:09PM +0100, Vincent Abriou wrote:
> >> In case no connector is found while creating the fbdev, gives the
> >> possibility to specify the default fbdev size by firstly checking if the
> >> command line is defining a preferred mode. Else go into fallback and set
> >> 1024x768 fbdev size as it was already done.
> >> 
> >> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> >> Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
> > 
> > btw on all this there's also the possible solution to delay setup of the
> > fbdev until the first connector switches to connected, and then only
> > allocting the fb and doing the setup. Tegra has that, and Thierry did some
> > patches to move that logic into the fb helpers. But there's some locking
> > issues that need to be fixed first, hence why those patches haven't landed
> > yet.
> > 
> > But if you never probe the right mode, this here sounds like a good idea
> > too.
> 
> The early creation of fbdev is useful for userland system. If fbdev
> creation is delayed until first connector is connected, userland systems
> startup could fails (like Android that check fbdev availability at startup).
> 
> Today if no connector is connected, a default 1024x768 fbdev is created
> but it does not necessarily match the targeted CRTC size. When the
> connector is connected, fbdev is not reconfigured with the targeted CRTC
> size and it is anyway too late for the userland to take into account new
> fbdev size. Reading the cmdline is an easy way to solve this.

Isn't it another case of working around userspace issue in the kernel ? 
Shouldn't the offending userspace code be fixed ? And while at it, moved from 
fbdev to DRM/KMS ? :-) I wrote a proof-of-concept patch a few years ago to use 
DRM/KMS in the Android init process. I'm sure it doesn't apply cleanly 
anymore, but I can share it if you're interested.

-- 
Regards,

Laurent Pinchart

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