[Mesa-dev] [PATCH 04/12] i965/fs/skl+: Use lcd2dms_w instead of lcd2dms

[Neil Roberts]

Ben Widawsky <ben at bwidawsk.net> writes:

>> +         /* On Gen9+ we'll use lcd2ms_w instead which has two registers for
>> +          * the MCS data.
>> +          */
>> +         if (op == SHADER_OPCODE_TXF_CMS_W) {
>> +            bld.MOV(retype(sources[length], BRW_REGISTER_TYPE_UD),
>> +                    mcs.file == IMM ?
>> +                    mcs :
>> +                    offset(mcs, bld, 1));
>> +            length++;
>> +         }
>
> This hunk is very confusing to me without more context from later patches. I
> assume the upper bits of mcs are 0 for the cases where you're doing < 16x, but
> there is no way to determine that.

Well, the documentation says that the upper bits of MCS are ignored when
the sample count is < 16, so it doesn't really matter if it's zeroed or
not. The MCS data is retrieved from ld_mcs which already returns 4 or 8
registers of data even before SKL. I guess I could add that to the
commit message.

> I am not a big fan of the, lay out all the infrastructure, then use it
> later, when it comes to patch review. Or am I missing something?

Hrm, I think for other patches I've had the opposite complaint so I
don't know what is best.

> (Also, I think a separate case for SHADER_OPCODE_TXF_CMS_W would
> probably look a bit nicer, but that's just a random thought).

Yes, you're probably right. I guess this patch is going to conflict with
your fast clear branch anyway so one of us will have to split it out at
that point :)

Regards,
- Neil