[Mesa-dev] Allocator Nouveau driver, Mesa EXT_external_objects, and DRM metadata import interfaces

[Ilia Mirkin]

On Wed, Dec 20, 2017 at 6:22 PM, Kristian Kristensen
<hoegsberg at google.com> wrote:
> On Wed, Dec 20, 2017 at 12:41 PM, Miguel Angel Vico <mvicomoya at nvidia.com>
> wrote:
>> On Wed, 20 Dec 2017 11:54:10 -0800
>> Kristian Høgsberg <hoegsberg at gmail.com> wrote:
>> > I'd like to see concrete examples of actual display controllers
>> > supporting more format layouts than what can be specified with a 64
>> > bit modifier.
>>
>> The main problem is our tiling and other metadata parameters can't
>> generally fit in a modifier, so we find passing a blob of metadata a
>> more suitable mechanism.
>
>
> I understand that you may have n knobs with a total of more than a total of
> 56 bits that configure your tiling/swizzling for color buffers. What I don't
> buy is that you need all those combinations when passing buffers around
> between codecs, cameras and display controllers. Even if you're sharing
> between the same 3D drivers in different processes, I expect just locking
> down, say, 64 different combinations (you can add more over time) and
> assigning each a modifier would be sufficient. I doubt you'd extract
> meaningful performance gains from going all the way to a blob.

There's probably a world of stuff that we don't know about in nouveau,
but I have a hard time coming up with more than 64-bits worth of
tiling info for dGPU surfaces...

There's 8 bits (sorta, not fully populated, but might as well use
them) of "micro" tiling which is done at the PTE level by the memory
controller and includes compression settings, and then there's 4 bits
of tiling per dimension for macro blocks (which configures different
sizes for each dimension for tile sizes) -- that's only 20 bits. MSAA
level (which is part of the micro tiling setting usually, but may not
necessarily have to be) - another couple of bits, maybe something else
weird for another few bits. Anyways, this is *nowhere* close to 64
bits.

What am I missing?

  -ilia