On Thu 11 May 2017, Jason Ekstrand wrote:
> On Thu, May 11, 2017 at 9:08 PM, Chad Versace <chadvers...@chromium.org>
> wrote:
>
> > On Thu 11 May 2017, Jason Ekstrand wrote:
> > > On Thu, May 11, 2017 at 7:03 AM, Pohjolainen, Topi <
> > > topi.pohjolai...@gmail.com> wrote:
> > >
> > > > On Wed, May 10, 2017 at 02:30:31PM -0700, Jason Ekstrand wrote:
> > > > > ---
> > > > > src/intel/isl/isl_gen6.c | 30 ++++++++++++------------------
> > > > > 1 file changed, 12 insertions(+), 18 deletions(-)
> > > > >
> > > > > diff --git a/src/intel/isl/isl_gen6.c b/src/intel/isl/isl_gen6.c
> > > > > index b746903..0de9620 100644
> > > > > --- a/src/intel/isl/isl_gen6.c
> > > > > +++ b/src/intel/isl/isl_gen6.c
> > > > > @@ -88,6 +88,8 @@ isl_gen6_choose_image_alignment_el(const struct
> > > > isl_device *dev,
> > > > > * | format | halign | valign |
> > > > > * +------------------------+--------+--------+
> > > > > * | YUV 4:2:2 formats | 4 | * |
> > > > > + * | BC1-5 | 4 | 4 |
> > > > > + * | FXT1 | 8 | 4 |
> > > > > * | uncompressed formats | 4 | * |
> > > > > * +------------------------+--------+--------+
> > > > > *
> > > > > @@ -110,29 +112,13 @@ isl_gen6_choose_image_alignment_el(const
> > struct
> > > > isl_device *dev,
> > > > > */
> > > > >
> > > > > if (isl_format_is_compressed(info->format)) {
> > > > > + /* Compressed formats have an alignment equal to their block
> > size
> > > > */
> > > > > *image_align_el = isl_extent3d(1, 1, 1);
> > > > > return;
> > > > > }
> > > > >
> > > > > - if (isl_format_is_yuv(info->format)) {
> > > > > - *image_align_el = isl_extent3d(4, 2, 1);
> > > > > - return;
> > > > > - }
> > > > > -
> > > > > - if (info->samples > 1) {
> > > > > - *image_align_el = isl_extent3d(4, 4, 1);
> > > > > - return;
> > > > > - }
> > > > > -
> > > > > - if (isl_surf_usage_is_depth_or_stencil(info->usage) &&
> > > > > - !ISL_DEV_USE_SEPARATE_STENCIL(dev)) {
> > > >
> > > > Maybe mention in the commit that we drop this as it is always false on
> > > > gen6+?
> > > > In isl.c: "dev->use_separate_stencil = ISL_DEV_GEN(dev) >= 6;"
> > > >
> > >
> > > No, I dropped it not because we always use separate stencil but because
> > > it's redundant with the regular depth case. The PRM says to use a 4x4
> > > alignment for all depth buffers but 4x2 for separate stencil. Combined
> > > depth-stencil falls under the "depth" case so I didn't think we needed to
> > > call it out explicitly.
> >
> > I admit that the condition I wrote
> >
> > if (isl_surf_usage_is_depth_or_stencil(info->usage) &&
> > !ISL_DEV_USE_SEPARATE_STENCIL(dev))
> >
> > was poorly chosen. I should've written it without relying on
> > ISL_DEV_USE_SEPARATE_STENCIL.
> >
> > Topi has a point because a surface with
> > format=ISL_FORMAT_X24_TYPELESS_G8_UINT will necessarily have
> > usage=ISL_SURF_USAGE_STENCIL_BIT (no depth bit). The hardware requires
> > the surface to have valign=4, and my badly written (but correct)
> > condition ensured valign=4 in this case. After this patch, the function
> > wrongly chooses valign=2.
> >
>
> No it won't. It's hard to see in patch form, but after this patch is
> applied we check for depth first and then stencil. If it has ANY depth
> component, then it will get 4x4 aligned. Only separate stencil gets 4x2.
This function, pre-patch and post-patch, does not inspect the format for
a depth component. It checks if the depth usage flag is set. That's the
key difference.
On gen6, it's possible to create a usable surface with format
X24_TYPELESS_G8_UINT with ISL_SURF_USAGE_STENCIL_BIT and no depth bit.
And, if I understand this patch correctly, that surface does not satisfy
the depth check in this patch:
if (isl_surf_usage_is_depth(info->usage)) {
/* depth buffer (possibly interleaved with stencil) */
*image_align_el = isl_extent3d(4, 4, 1);
return;
}
Instead, that surface eventually hits this at the bottom of the
function:
*image_align_el = isl_extent3d(4, 2, 1);
Of course, such a surface is only usable as a stencil buffer if hiz is
disabled. So we'll probably never observe such a surface in real life.
But we should at least assert that's the case.
> > I suggest either
> >
> > a. Asserting that separate stencil is true in the neighborhood of
> >
> > if (isl_surf_usage_is_depth(info->usage)) {
> > /* depth buffer (possibly interleaved with stencil) */
> > *image_align_el = isl_extent3d(4, 4, 1);
> > return;
> > }
> >
> > and dropping the reference to possible interleaved stencil.
> >
> > b. Or, better, rewrite the original logic to be clearer.
> >
> > if ((info->usage & ISL_SURF_USAGE_STENCIL_BIT)
> > && info->format == ISL_FORMAT_R8_UINT) {
> > /* separate stencil surface */
> > *image_align_el = isl_extent3d(4, 2, 1);
> > return;
> > }
> >
> > if (info->usage & (ISL_SURF_USAGE_DEPTH_BIT |
> > ISL_SURF_USAGE_STENCIL_BIT))
> > /* separate depth surface or interleaved depthstencil */
> > *image_align_el = isl_extent3d(4, 4, 1);
> > return;
> > }
> >
> > > > Other than that:
> > > >
> > > > Reviewed-by: Topi Pohjolainen <topi.pohjolai...@intel.com>
> > > >
> > > > > - /* interleaved depthstencil buffer */
> > > > > - *image_align_el = isl_extent3d(4, 4, 1);
> > > > > - return;
> > > > > - }
> > > > > -
> > > > > if (isl_surf_usage_is_depth(info->usage)) {
> > > > > - /* separate depth buffer */
> > > > > + /* depth buffer (possibly interleaved with stencil) */
> > > > > *image_align_el = isl_extent3d(4, 4, 1);
> > > > > return;
> > > > > }
> > > > > @@ -143,5 +129,13 @@ isl_gen6_choose_image_alignment_el(const struct
> > > > isl_device *dev,
> > > > > return;
> > > > > }
> > > > >
> > > > > + if (info->samples > 1) {
> > > > > + *image_align_el = isl_extent3d(4, 4, 1);
> > > > > + return;
> > > > > + }
> > > > > +
> > > > > + /* For everything else, we can chose any vertical alignment we
> > > > want. We
> > > > > + * choose an alignment of 2 because it uses the least memory.
> > > > > + */
> > > > > *image_align_el = isl_extent3d(4, 2, 1);
> >
> > The code is correct, but the comment is wrong. We cannot choose any
> > valign we wish for the remaining cases. It is true that 2 is *valid* for
> > all remaining cases, but it is also *required* for some of those cases,
> > as explained in the big comment block above. Namely, all render target
> > surfaces and also separate stencil require valign=2.
> >
>
> Hrm... Ok, I'll try and come up with a better comment.
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