[PATCH] drm/gma500: Add CedarView LVDS blacklist

[Patrik Jakobsson]

On Wed, Apr 10, 2019 at 11:09 AM Hans de Goede <hdegoede at redhat.com> wrote:
>
> Hi,
>
> On 10-04-19 11:00, Patrik Jakobsson wrote:
> > On Wed, Apr 10, 2019 at 9:27 AM Hans de Goede <hdegoede at 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 at 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 at 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, but I assume there are CedarView based laptops with LVDS panels
> which works, so I suspect this might be more of a bug in your BIOS.

I was thinking of the case where LVDS is disabled. Things work fine
when there actually is a panel present.

>
> So what is the next step in debugging this?

I'll give Villes suggestion a try.

>
> Regards,
>
> Hans
>