On Tue, Sep 22, 2015 at 4:18 PM, Ben Widawsky <b...@bwidawsk.net> wrote:
> On Thu, Sep 17, 2015 at 05:00:11PM +0100, Neil Roberts wrote: > > In order to accomodate 16x MSAA, the starting sample pair index is now > > 3 bits rather than 2 on SKL+. > > Hooray for bad docs. "PS Thread Payload for Normal Dispatch": SSPI is 2 > bits > (R0.0.7:6) with 1 reserved for expansion. > > > --- > > src/mesa/drivers/dri/i965/brw_fs.cpp | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp > b/src/mesa/drivers/dri/i965/brw_fs.cpp > > index 82f49b4..bd9bcdd 100644 > > --- a/src/mesa/drivers/dri/i965/brw_fs.cpp > > +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp > > @@ -1300,9 +1300,16 @@ fs_visitor::emit_sampleid_setup() > > * are sample 1 of subspan 0; the third group is sample 0 of > > * subspan 1, and finally sample 1 of subspan 1. > > */ > > + > > + /* SKL+ has an extra bit for the Starting Sample Pair Index to > > + * accomodate 16x MSAA. > > + */ > > + unsigned sspi_bits = devinfo->gen >= 9 ? 3 : 2; > > + unsigned sspi_mask = ((1 << sspi_bits) - 1) << 6; > > + > > I think using the bits makes this unnecessarily hard to read. > unsigned sspi_mask = devinfo->gen >= 9 ? 0x1c0 : 0xc0; > > > abld.exec_all() > > .AND(t1, fs_reg(retype(brw_vec1_grf(0, 0), > BRW_REGISTER_TYPE_UD)), > > - fs_reg(0xc0)); > > + fs_reg(sspi_mask)); > > abld.exec_all().SHR(t1, t1, fs_reg(5)); > > > > /* This works for both SIMD8 and SIMD16 */ > > I'm really sketchy on the details of how this actually works. Mostly, I > get what > this code is doing, and I agree that the only difference for 16x should be > the > extra bit (because SSPI needs to go up to 7 for SIMD8). > As per docs we're supposed to get the per slot SampleID written to 15:0 bits in R1.0. I used SSPI to compute the SampleID because I never got anything useful in these bits on IVB. Things might have changed on later platforms. So, I think it's worth trying to do what docs say. I'll send out a patch to add above reasoning as a comment in this code. For now I'm happy with this patch: Reviewed-by: Anuj Phogat <anuj.pho...@gmail.com> > > So take my: > Reviewed-by: Ben Widawsky <b...@bwidawsk.net> > > with a grain of salt. > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/mesa-dev >
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