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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 10, 2019 at 11:00:23AM +0200, Patrik Jakobsson wrote:
> On Wed, Apr 10, 2019 at 9:27 AM Hans de Goede <hdegoede@redhat.com> wrote:
> >
> > Hi,
> >
> > On 09-04-19 21:31, Dominik 'Rathann' Mierzejewski wrote:
> > > 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.
> >
> > To be clear what Dominik means here is that he has a VGA monitor
> > connected. There is no LVDS panel in this device at all.
> 
> Thanks for testing. I dusted off my DN2800MT and tried turning LVDS
> on/off in the BIOS. With LVDS disabled gma500 reports it as connected.
> When LVDS is enabled in bios I instead get a connected eDP connector.
> I'm starting to think that broken VBT parsing might be the actual
> problem.

Maybe try something like what I did in ca3b3fa34447 ("drm/i915: Consult
VBT "LVDS config" bits to determine whether internal LVDS is present") ?

Not that I know for sure that it actually works. So far we've had no
reports of the WARN I added. So either no one has tested a recent kernel
with any machine on the current DMI list, or my entire idea of trusting
the LVDS config bits is nonsense.

-- 
Ville Syrjälä
Intel
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