[Mesa-dev] [PATCH] i965/gen9: use an unreserved surface alignment value

[Nanley Chery]

On Thu, Jun 25, 2015 at 12:37 AM, Pohjolainen, Topi
<topi.pohjolainen at intel.com> wrote:
> On Wed, Jun 24, 2015 at 05:57:13PM -0700, Anuj Phogat wrote:
>> On Wed, Jun 24, 2015 at 3:51 PM, Nanley Chery <nanleychery at gmail.com> wrote:
>> > From: Nanley Chery <nanley.g.chery at intel.com>
>> >
>> > Although the horizontal and vertical alignment fields are ignored here,
>> > 0 is a reserved value for them and may cause undefined behavior. Change
>> > the default value to an abitrary valid one.
>> >
>> > Signed-off-by: Nanley Chery <nanley.g.chery at intel.com>
>> > ---
>> >  src/mesa/drivers/dri/i965/gen8_surface_state.c | 4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/src/mesa/drivers/dri/i965/gen8_surface_state.c b/src/mesa/drivers/dri/i965/gen8_surface_state.c
>> > index b2d1a57..22ae960 100644
>> > --- a/src/mesa/drivers/dri/i965/gen8_surface_state.c
>> > +++ b/src/mesa/drivers/dri/i965/gen8_surface_state.c
>> > @@ -93,7 +93,7 @@ vertical_alignment(const struct brw_context *brw,
>> >     if (brw->gen > 8 &&
>> >         (mt->tr_mode != INTEL_MIPTREE_TRMODE_NONE ||
>> >          surf_type == BRW_SURFACE_1D))
>> > -      return 0;
>> > +      return GEN8_SURFACE_VALIGN_4;
>> >
>> >     switch (mt->align_h) {
>> >     case 4:
>> > @@ -118,7 +118,7 @@ horizontal_alignment(const struct brw_context *brw,
>> >     if (brw->gen > 8 &&
>> >         (mt->tr_mode != INTEL_MIPTREE_TRMODE_NONE ||
>> >          gen9_use_linear_1d_layout(brw, mt)))
>> > -      return 0;
>> > +      return GEN8_SURFACE_HALIGN_4;
>> >
>> >     switch (mt->align_w) {
>> >     case 4:
>> > --
>> > 2.4.4
>> >
>> > _______________________________________________
>> > mesa-dev mailing list
>> > mesa-dev at lists.freedesktop.org
>> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
>> Good find Nanley. We had no known issues with value 0 but it's
>> always nice to avoid undefined behavior :).
>
> Right, I thought about this when I reviewed the original. The spec says
> it is ignored in these cases and hence the reserved value seemed fine. Now
> that we put something meaningful there, somebody is going to compare the
> spec and wonder why we set it to 4. If we added also a comment here that
> says this is just an arbitrary (non-reserved) value and really ignored
> by the hardware, it would prevent misunderstandings. What do you guys think?
>
There's enough space to insert "Set to an arbitrary non-reserved
value." in both of the comments preceding the conditional without
adding an extra line. I wouldn't mind including it.

Thanks,
Nanley