[Mesa-dev] [PATCH] i965: Fix regression in depth texture rendering on pre-SNB

[Kenneth Graunke]

On 10/19/2012 02:11 PM, Ian Romanick wrote:
> From: Ian Romanick <ian.d.romanick at intel.com>
>
> This was introduced by commit 24db6d6 (cherry-picked from a683012).  The
> original patch fixed potential GPU hangs on SNB, and it caused some
> rendering regressions there.  The benefits outweigh the costs.
>
> However, the work-around is not necessary for pre-SNB chipsets.
> Applying the work-around there gives rendering regressions with no
> benefit.  This patch disables the work-around on pre-SNB chipsets.
>
> NOTE: This is a candidate for the 8.0 and 9.0 branches

Well.  The docs have always said:

"The 3 LSBs of both offsets must be zero to ensure correct alignment" 
(G45 Vol 2 Page 280).

So not following that is always wrong, even on pre-Gen6.  But somehow, 
it always seemed to work out...until we turned on HiZ.

I am OK with applying this to the 8.0 branch, as it restores the old 
behavior that we shipped for ages, and shouldn't cause GPU hangs.  You 
can add my Acked-by to that.

However, I am opposed to applying it to the 9.0 branch.  Eric has an 
actual fix for depth rendering to small miplevels, and I'd rather see 
that backported.  I don't know if it's landed yet though.

> ---
>   src/mesa/drivers/dri/i965/brw_misc_state.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_misc_state.c b/src/mesa/drivers/dri/i965/brw_misc_state.c
> index 6dfa08e..4799af2 100644
> --- a/src/mesa/drivers/dri/i965/brw_misc_state.c
> +++ b/src/mesa/drivers/dri/i965/brw_misc_state.c
> @@ -413,8 +413,10 @@ static void emit_depthbuffer(struct brw_context *brw)
>          * tile_x and tile_y to 0.  This is a temporary workaround until we come
>          * up with a better solution.
>          */
> -      tile_x &= ~7;
> -      tile_y &= ~7;
> +      if (intel->gen >= 6) {
> +         tile_x &= ~7;
> +         tile_y &= ~7;
> +      }
>
>         BEGIN_BATCH(len);
>         OUT_BATCH(_3DSTATE_DEPTH_BUFFER << 16 | (len - 2));