[Nouveau] [PATCH] drm/nouveau: rewrite nouveau_dma_wait()

[Pekka Paalanen]

On Sat, 22 Aug 2009 12:30:03 +0200
Maarten Maathuis <madman2003 at gmail.com> wrote:

> dma.max is adjusted to always have space for the jump.

Ah, then that should be documented somewhere.

But if that is the case, why:
>>> chan->dma.free = get - chan->dma.cur - 1;

The extra space is not needed in this branch, since the available space
is limited by GET. If it is not locked up, GET will move forward and give
space. Otherwise, we would be in the get <= dma.cur branch.

Assuming the jump command is at index dma.max, isn't dma.max the maximum
possible value for GET inside the ring? Therefore
>>> chan->dma.free = get - chan->dma.cur - 1;
should become equivalent to
>>> chan->dma.free = chan->dma.max - chan->dma.cur;
but there is the -1.

Or do we observe GET == dma.max + 1 just before it actually jumps?

Or do we simply not know how it behaves and want to be safe?

-- 
Pekka Paalanen
http://www.iki.fi/pq/