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

[Jani Nikula]

On Fri, 10 Feb 2017, Hans de Goede <hdegoede at redhat.com> wrote:
> On 06-02-17 08:04, Jani Nikula wrote:
>> First, I want a big fat warning comment about what's going on
>> here. Otherwise someone's bound to "fix" this later on.
>
> Done for v2, which I will send shortly.

Thanks.

>> Second, per the spec, the ASLE ext mailbox is 1k in size, and there's a
>> 1k reserved region at the end. We probably shouldn't allow VBT to extend
>> over there. But hey, per the spec we also shouldn't allow VBT to extend
>> over mailbox #5 either. So if you can't be bothered with that, neither
>> will I.
>
> Hmm, that makes no sense, OPREGION_SIZE is 8192 bytes or 0x2000,
> OPREGION_ASLE_EXT_OFFSET is 0x1C00 or 7168 bytes, if there is 1k
> reserved after the ASLE ext mailbox then there is exactly 0 bytes
> available for the ASLE ext mailbox or OPREGION_SIZE should be 9216
> not 8192 (which I don't think so). Maybe the last 1k is either
> the ASLE ext mailbox OR reserved ?

You're quite right, that makes no sense. :) Looks like we account for
the reserved part at the end of struct opregion_asle_ext, but the spec
isn't quite clear whether the reserved part is actually part of the
mailbox or not. I'm not quite sure how I managed to confuse myself to
turn that into 1k. Sorry.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center