[Intel-gfx] [PATCH] drm/i915: Fix not finding the VBT when it overlaps with OPREGION_ASLE_EXT

Jani Nikula jani.nikula at linux.intel.com
Tue Jan 24 13:33:13 UTC 2017

On Mon, 23 Jan 2017, Hans de Goede <hdegoede at redhat.com> wrote:
> Hi,
> On 23-01-17 11:36, Jani Nikula wrote:
>> On Fri, 20 Jan 2017, Hans de Goede <hdegoede at redhat.com> wrote:
>>> Hi,
>>> On 31-12-16 17:00, Hans de Goede wrote:
>>>> Hi,
>>>> On 27-12-16 11:58, Jani Nikula wrote:
>>>>> On Sun, 25 Dec 2016, Hans de Goede <hdegoede at redhat.com> wrote:
>>>>>> If there is no OPREGION_ASLE_EXT then a VBT stored in mailbox #4 may
>>>>>> use the ASLE_EXT parts of the opregion. Adjust the vbt_size calculation
>>>>>> for a vbt in mailbox #4 for this.
>>>>>> This fixes the driver not finding the VBT on a jumper ezpad mini3
>>>>>> cherrytrail tablet.
>>>>> Thanks for the patch. I think you're onto something, but I don't think
>>>>> the patch is quite correct. That said, I'm not sure myself yet what
>>>>> would be. ;)
>>>>> Without the change, does intel_bios_is_valid_vbt() return true anyway?
>>>> No.
>>>>> I.e. do you get "Found valid VBT in ACPI OpRegion (Mailbox #4)\n" in
>>>>> log?
>>>> No.
>>>>> If not, which of the debug messages in intel_bios_is_valid_vbt() do
>>>>> you get?
>>>> I get "BDB incomplete", which is why I wrote this patch and believe
>>>> this patch is the right solution. With this patch everything works,
>>>>> In the latter case, I suspect you'll end up with failure in intel_bios.c
>>>>> with either "No MIPI config BDB found" or "No MIPI Sequence found,
>>>>> parsing complete\n".
>>>> I don't remember the exact error, other then getting the
>>>> "BDB incomplete" error, and the i915 driver not listing the DSI connector
>>>> under /sys/class drm.
>>>> What makes you say: "but I don't think the patch is quite correct" why
>>>> should the code still keep the OPREGION_ASLE_EXT start as end of the
>>>> mailbox #4 vbt if there is the ASLE extenstion is not used ?
>>> Ping, any progress on this ? I still believe my original patch is
>>> correct. Eitherway I would like to see a fix for this, be it this fix
>>> or something else, as a fix is necessary to get the LCD panel to work
>>> on jumper ezpad mini3 tablets.
>> Please send me /sys/kernel/debug/dri/0/i915_opregion on that machine.
>> Perusing the opregion spec (which I regret I can't share with you), I
>> found this:
>> * On mailboxes in general, "Mail-box locations are fixed and should
>>   always be allocated irrespective of the support for a given mail box
>>   is available or not."
>> * On opregion->asle->rvda, "This is mainly used when VBT size exceeds
>>   6KB and can't be stored in Mailbox4." It isn't clear to me whether
>>   ->rvda was used or not. The opregion dump should shed light on
>>   this. You can of course check that by adding debug prints in the code
>>   too.
>> * On mailbox 4 (the VBT), "Holds a maximum of 6KB sized Raw VBT data
>>   (not VBIOS image) from VBIOS image."
>> Clearly the patch is against the spec. Let's see if the opregion you
>> have there is against the spec too, and proceed from there...
> Ok, I've attached a dump of the opregion on the tablet in question.

Thanks. rvda is not used, VBT is in in the mailbox, and reports size
0x1843, i.e. 67 bytes over the mailbox size of 6 kB. *facepalm*.

I'll try to ask around to see if someone knows what they were thinking.


> Regards,
> Hans

Jani Nikula, Intel Open Source Technology Center

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