src/panfrost/midgard/midgard_errata_lod.c

/*
 * Copyright (C) 2019 Collabora, Ltd.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "compiler/nir/nir.h"
#include "compiler/nir/nir_builder.h"

bool midgard_nir_lod_errata(nir_shader *shader);

/* Workarounds errata pertaining to early Midgard chips where the settings for
 * min_lod/max_lod/lod_bias are ignored in the sampler descriptor when
 * texturing with a textureLod instruction. The workaround is to load these
 * constants in as system values and perform the bias/clamp in the shader.
 */

static void
mir_lod_errata_body(nir_builder *b, nir_tex_instr *tex)
{
        /* The errata only applies to textureLod ("TEXGRD") */
        if (tex->op != nir_texop_txl)
                return;

        /* Let's grab the sampler parameters */
        nir_intrinsic_instr *l = nir_intrinsic_instr_create(b->shader,
                        nir_intrinsic_load_sampler_lod_parameters_pan);
        l->num_components = 3;
        nir_ssa_dest_init(&l->instr, &l->dest, 3, 32, NULL);

        /* TODO: Indirect samplers, separate sampler objects XXX */
        nir_src idx = nir_src_for_ssa(nir_imm_int(b, tex->texture_index));
        nir_src_copy(&l->src[0], &idx, l);

        nir_builder_instr_insert(b, &l->instr);
        nir_ssa_def *params = &l->dest.ssa;

        /* Extract the individual components */
        nir_ssa_def *min_lod = nir_channel(b, params, 0);
        nir_ssa_def *max_lod = nir_channel(b, params, 1);
        nir_ssa_def *lod_bias = nir_channel(b, params, 2);
        
        /* Rewrite the LOD with bias/clamps. Order sensitive. */
        for (unsigned i = 0; i < tex->num_srcs; i++) {
                if (tex->src[i].src_type != nir_tex_src_lod)
                        continue;

                nir_ssa_def *lod = nir_ssa_for_src(b, tex->src[i].src, 1);

                nir_ssa_def *biased = nir_fadd(b, lod, lod_bias);
                nir_ssa_def *clamped = nir_fmin(b,
                                nir_fmax(b, biased, min_lod), max_lod);

                nir_instr_rewrite_src(&tex->instr, &tex->src[i].src,
                                nir_src_for_ssa(clamped));
        }
}

bool
midgard_nir_lod_errata(nir_shader *shader)
{
        nir_foreach_function(function, shader) {
                if (!function->impl) continue;

                nir_builder b;
                nir_builder_init(&b, function->impl);

                nir_foreach_block(block, function->impl) {
                        nir_foreach_instr_safe(instr, block) {
                                if (instr->type != nir_instr_type_tex) continue;

                                nir_tex_instr *tex = nir_instr_as_tex(instr);
                                b.cursor = nir_before_instr(instr);
                                mir_lod_errata_body(&b, tex);
                        }
                }

                nir_metadata_preserve(function->impl, nir_metadata_block_index | nir_metadata_dominance);

        }
        return true;
}