[Mesa-dev] [PATCH 02/17] i965/miptree: Zero-initialize CCS_D buffers

[Jason Ekstrand]

Good catch. Rb

On May 3, 2018 12:04:59 Nanley Chery <nanleychery at gmail.com> wrote:

> Before this patch, the aux_state was actually AUX_INVALID because the BO
> was never defined. This was fine on single slice miptrees because we
> would fast-clear the resource right after creation. For multi-slice
> miptrees on SKL+ however, this results in undefined behavior when
> accessing a non-base slice. Here's a specific example:
>
> 1) Fast clear level 0
>   * Undefined CCS_D buffer allocated in "PASS_THROUGH" state.
>   * Level 0 transitions to the CLEAR state.
> 2) Render to level 1
>   * Level 1 may have a 2-bit pattern of 2's.
>   * Rendering with a 2 in the CCS is undefined.
>
> Cc: <mesa-stable at lists.freedesktop.org>
> ---
> src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c 
> b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> index 377efae32c9..182a896e23a 100644
> --- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> +++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
> @@ -1806,13 +1806,11 @@ intel_miptree_alloc_ccs(struct brw_context *brw,
>     * A CCS value of 0 indicates that the corresponding block is in the
>     * pass-through state which is what we want.
>     *
> -    * For CCS_D, on the other hand, we don't care as we're about to perform a
> -    * fast-clear operation.  In that case, being hot in caches more useful.
> +    * For CCS_D, do the same thing. On gen9+, this avoids having any undefined
> +    * bits in the aux buffer.
>     */
> -   const uint32_t alloc_flags = mt->aux_usage == ISL_AUX_USAGE_CCS_E ?
> -                                BO_ALLOC_ZEROED : BO_ALLOC_BUSY;
> -   mt->aux_buf = intel_alloc_aux_buffer(brw, "ccs-miptree",
> -                                        &temp_ccs_surf, alloc_flags, mt);
> +   mt->aux_buf = intel_alloc_aux_buffer(brw, "ccs-miptree", &temp_ccs_surf,
> +                                        BO_ALLOC_ZEROED, mt);
>    if (!mt->aux_buf) {
>       free(aux_state);
>       return false;
> --
> 2.16.2
>
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