[Mesa-dev] [PATCH 10/11] freedreno: a2xx: split large draws on a20x

[Ilia Mirkin]

By the way, apparently VC4 has this restriction as well. Eric Anholt
covered more primitives in his logic, but also skipped trifans:

https://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/drivers/vc4/vc4_draw.c#n431

I think it's worth copying some of that in here, or if you're feeling
generous, making a shared helper that can be used in both places.

Cheers,

  -ilia

On Mon, Sep 17, 2018 at 3:36 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Mon, Sep 17, 2018 at 2:22 PM, Jonathan Marek <jonathan at marek.ca> wrote:
>> a20x can only draw 65535 vertices at once. this fix only applies to
>> triangles.
>>
>> Signed-off-by: Jonathan Marek <jonathan at marek.ca>
>> ---
>>  src/gallium/drivers/freedreno/a2xx/fd2_draw.c | 30 +++++++++++++++++--
>>  1 file changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/gallium/drivers/freedreno/a2xx/fd2_draw.c b/src/gallium/drivers/freedreno/a2xx/fd2_draw.c
>> index 1792505808..7ccbee587f 100644
>> --- a/src/gallium/drivers/freedreno/a2xx/fd2_draw.c
>> +++ b/src/gallium/drivers/freedreno/a2xx/fd2_draw.c
>> @@ -171,8 +171,34 @@ fd2_draw_vbo(struct fd_context *ctx, const struct pipe_draw_info *pinfo,
>>         fd2_emit_state(ctx, ctx->batch->draw, ctx->dirty);
>>         fd2_emit_state(ctx, ctx->batch->binning, ctx->dirty);
>>
>> -       draw_impl(ctx, pinfo, ctx->batch->draw, index_offset, false);
>> -       draw_impl(ctx, pinfo, ctx->batch->binning, index_offset, true);
>> +       /* a20x can only draw 65535 vertices at once... */
>> +       if (is_a20x(ctx->screen) && pinfo->count > 0xffff) {
>> +               struct pipe_draw_info info = *pinfo;
>> +               unsigned count = info.count;
>> +               unsigned num_vertices = ctx->batch->num_vertices;
>> +
>> +               /* other primitives require more work
>> +                * (triangles works because 0xffff is divible by 3)
>> +                */
>> +               if (info.mode != PIPE_PRIM_TRIANGLES)
>
> Should be fine for POINTS too, no?
>
> Other primitives require incrementally more work ...
>
> LINES: use 0xfffe.
> TRIANGLE_STRIP/LINE_STRIP: back up info->start by 2/1 vertices, and
> draw an extra primitive.
> TRI_FAN: not easy :( could probably do something with an index buffer.
>
> Hopefully primitive restart isn't enabled for a2xx...
>
>> +                       return false;
>> +
>> +               for (; count; ) {
>> +                       info.count = MIN2(count, 0xffff);
>> +
>> +                       draw_impl(ctx, &info, ctx->batch->draw, index_offset, false);
>> +                       draw_impl(ctx, &info, ctx->batch->binning, index_offset, true);
>> +
>> +                       info.start += 0xffff;
>> +                       ctx->batch->num_vertices += 0xffff;
>
> Should both of these be += info.count? And then you don't need the
> ->num_vertices = num_vertices hack at the end?
>
>> +                       count -= info.count;
>> +               }
>> +               /* changing this value is a hack, restore it */
>> +               ctx->batch->num_vertices = num_vertices;
>> +       } else {
>> +               draw_impl(ctx, pinfo, ctx->batch->draw, index_offset, false);
>> +               draw_impl(ctx, pinfo, ctx->batch->binning, index_offset, true);
>> +       }
>>
>>         fd_context_all_clean(ctx);
>>
>> --
>> 2.17.1
>>
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