Re: [PATCH] drm/gma500: Add CedarView LVDS blacklist

From: Dominik 'Rathann' Mierzejewski <dominik@greysector.net>
To: Hans de Goede <hdegoede@redhat.com>
Cc: David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel.vetter@intel.com>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm/gma500: Add CedarView LVDS blacklist
Date: Tue, 9 Apr 2019 21:31:55 +0200	[thread overview]
Message-ID: <20190409193155.GA30275@sakura.greysector.net> (raw)
In-Reply-To: <42467064-1ac3-19eb-344f-af0da225c7bf@redhat.com>

Hello,

On Tuesday, 09 April 2019 at 16:44, Hans de Goede wrote:
> Hi,
> 
> On 09-04-19 14:05, Patrik Jakobsson wrote:
> > On Tue, Apr 9, 2019 at 12:20 PM Hans de Goede <hdegoede@redhat.com> wrote:
> > > 
> > > Hi,
> > > 
> > > On 09-04-19 11:47, Patrik Jakobsson wrote:
> > > > On Tue, Apr 9, 2019 at 8:51 AM Hans de Goede <hdegoede@redhat.com> wrote:
> > > > > 
> > > > > Some CedarView VBT-s claim that there is a LVDS panel, while there is none.
> > > > > Specifically this happens on the Thecus N2800 / N5550 NAS models.
> > > > > 
> > > > > This commit adds a LVDS blacklist to deal with this and adds an entry for
> > > > > the Thecus NAS-es.
> > > > 
> > > > Hi Hans,
> > > > Sometimes LVDS can be configured in the BIOS on CDV devices. Can you
> > > > check that it's not just a bad BIOS configuration first?
> > > 
> > > I've asked the reporter to test, but even if there is a BIOS option it
> > > seems that the BIOS default setting is wrong and we cannot expect every
> > > user to go into the BIOS to fix a wrong BIOS setting.
> > > 
> > > According to this blogpost, which is about the Linux the device ships with:
> > > https://astroweasel.blogspot.com/2016/02/updating-thecus-n5550-nas-to-report.html
> > > 
> > > The pre-installed grub config includes 'video=LVDS-1:d' on the kernel
> > > commandline, so this clearly seems to be a case where the system is just
> > > shipping with a broken BIOS or at least with default BIOS settings which
> > > is just as bad.
> > 
> > I agree that we should try to fix a broken default but are you sure
> > this will only affect the n5550? IIUC Milstead / Granite Well is an
> > Intel product / board name and perhaps some of those use LVDS.
> 
> Milstead is the name of Intel's NAS reference design:
> 
> https://www.hardwarezone.com.my/tech-news-intel-unveils-milstead-platform-nas-devices
> 
> I seriously doubt that any NAS-es have a LVDS (laptop/tablet) LCD panel.
> 
> > Also, if the pre-installed OS solves this on the cmdline then it's
> > only a problem if the user is trying to install a custom OS on the
> > device. I would expect such a user to be able to change bios settings.
> > 
> > I'm not totally against this but not sure about the consequences. Is
> > there perhaps a better dmi string to match against?
> 
> No there are no better DMI strings to match against I'm afraid.

I did load default settings in BIOS setup and there's no change in
behaviour. LVDS gets detected as connected:
$ cat /sys/class/drm/card0-LVDS-1/status 
connected

Only VGA output is physically connected at the moment.

Regards,
Dominik
-- 
Fedora   https://getfedora.org  |  RPM Fusion  http://rpmfusion.org
There should be a science of discontent. People need hard times and
oppression to develop psychic muscles.
        -- from "Collected Sayings of Muad'Dib" by the Princess Irulan
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