[Mesa-dev] [PATCH 1/7] ac/surface: handle DCC subresource fast clear restriction on VI

[Marek Olšák]

On Fri, Apr 27, 2018 at 4:14 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:

> Sorry, but I still don't understand the logic of this :/
>
> What we want to check for is that all the DCC bytes of a mip-level are
> contiguous, right?
>
> Why does it matter for that whether a level is the last level?
>
> Here's the thought experiment that I can't make sense of: Let's say that
> you have format, base level, and number of levels N so that the last-level
> condition applies. That is, all levels up to and including N-2 have
> dccRamAligned true. Level N-1 has dccRamAligned false, but the patch as-is
> will still consider it fast-clearable.
>

Yes, because the non-contiguous level N-1 DCC range (last level) doesn't
overlap with any existing level. It's interleaved with level N that doesn't
exist. So clearing the level N-1 DCC range that might overwrite level N DCC
range doesn't break anything and so the clear is allowed.

Is it clear now?

Marek
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