[Mesa-dev] [PATCH 2/6] i965/fs: Enumerate logical fb writes arguments

[Matt Turner]

On Tue, Oct 20, 2015 at 3:11 PM, Ben Widawsky <ben at bwidawsk.net> wrote:
> On Tue, Oct 20, 2015 at 02:57:24PM -0700, Matt Turner wrote:
>> On Tue, Oct 20, 2015 at 2:54 PM, Ben Widawsky <ben at bwidawsk.net> wrote:
>> > On Tue, Oct 20, 2015 at 02:52:29PM -0700, Matt Turner wrote:
>> >> On Tue, Oct 20, 2015 at 2:29 PM, Ben Widawsky
>> >> <benjamin.widawsky at intel.com> wrote:
>> >> > Gen9 adds the ability to write out a stencil value, so we need to expand the
>> >> > virtual payload by one. Abstracting this now makes that change easier to read.
>> >> >
>> >> > I was admittedly confused early on about some of the hardcoding. If people
>> >> > believe the resulting code is inferior, I am not super attached to the patch.
>> >> >
>> >> > Cc: Francisco Jerez <currojerez at riseup.net>
>> >> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
>> >> > ---
>> >> >  src/mesa/drivers/dri/i965/brw_defines.h | 18 ++++++++++--------
>> >> >  src/mesa/drivers/dri/i965/brw_fs.cpp    | 21 +++++++++++----------
>> >> >  2 files changed, 21 insertions(+), 18 deletions(-)
>> >> >
>> >> > diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
>> >> > index 7a5ee1b..e06c9d6 100644
>> >> > --- a/src/mesa/drivers/dri/i965/brw_defines.h
>> >> > +++ b/src/mesa/drivers/dri/i965/brw_defines.h
>> >> > @@ -912,14 +912,6 @@ enum opcode {
>> >> >     /**
>> >> >      * Same as FS_OPCODE_FB_WRITE but expects its arguments separately as
>> >> >      * individual sources instead of as a single payload blob:
>> >> > -    *
>> >> > -    * Source 0: [required] Color 0.
>> >> > -    * Source 1: [optional] Color 1 (for dual source blend messages).
>> >> > -    * Source 2: [optional] Src0 Alpha.
>> >> > -    * Source 3: [optional] Source Depth (gl_FragDepth)
>> >> > -    * Source 4: [optional (gen4-5)] Destination Depth passthrough from thread
>> >> > -    * Source 5: [optional] Sample Mask (gl_SampleMask).
>> >> > -    * Source 6: [required] Number of color components (as a UD immediate).
>> >> >      */
>> >> >     FS_OPCODE_FB_WRITE_LOGICAL,
>> >> >
>> >> > @@ -1318,6 +1310,16 @@ enum brw_urb_write_flags {
>> >> >        BRW_URB_WRITE_ALLOCATE | BRW_URB_WRITE_COMPLETE,
>> >> >  };
>> >> >
>> >> > +enum fb_write_logical_args {
>> >> > +   FB_WRITE_COLOR0 = 0,      /* REQUIRED */
>> >> > +   FB_WRITE_COLOR1 = 1,      /* for dual source blend messages */
>> >> > +   FB_WRITE_SRC0_ALPHA = 2,
>> >> > +   FB_WRITE_SRC_DEPTH = 3,   /* gl_FragDepth */
>> >> > +   FB_WRITE_DST_DEPTH = 4,   /* GEN4-5: passthrough from thread */
>> >> > +   FB_WRITE_OMASK = 5,       /* Sample Mask (gl_SampleMask) */
>> >> > +   FB_WRITE_COMPONENTS = 6,  /* REQUIRED */
>> >>
>> >> Do we gain anything by assigning values explicitly?
>> >
>> > Just code readability. As a noob coming into the code, seeing a random "6" or
>> > "4" in places was strange and it took a bit to figure out where to get the
>> > sensible value from.
>> >
>> > Is there any specific opposition toward doing this, or some reason it wasn't
>> > done in the first place? I honestly don't care too much...
>>
>> If everything just uses the new enum values (and their values don't
>> matter per se), we shouldn't assign them specifically. Patch 4/6 would
>> be simpler if you didn't have to renumber some of the enums, for
>> instance.
>
> Yes, I suppose patch 4/6 does end up without the first hunk in the patch if I
> did away with this, but I still think the readability gained outweighs that.
> However, I admit my knowledge in this part of the codebase is likely the
> minority (in between 0 and expert).

What I should have said in the previous email is that assigning
arbitrary numbers to enums in brw_defines.h is confusing because one
might be led to believe that these are hardware values (like almost
everything else is in brw_defines.h).