[PATCH] drm/gma500: Add CedarView LVDS blacklist

[Hans de Goede]

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.

So what is the next step in debugging this?

Regards,

Hans