Quoting Tvrtko Ursulin (2018-02-21 13:35:38)
>
> On 21/02/2018 13:07, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-02-21 12:55:17)
> >>
> >> On 21/02/2018 12:53, Tvrtko Ursulin wrote:
> >>>
> >>> On 21/02/2018 12:17, Chris Wilson wrote:
> >>>> How much do I want this uABI to rot away? Say "Never again!" to implicit
> >>>> aliasing.
> >>>>
> >>>> In the meantime, we do not need to perform duplicate work on bsd2
> >>>> machines, as especially we do not know which engine bsd relates to.
> >>>>
> >>>> v2: When in doubt, shout!
> >>>>
> >>>> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >>>> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >>>> ---
> >>>> lib/ioctl_wrappers.c | 2 +-
> >>>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
> >>>> index 8748cfcf..b9b86079 100644
> >>>> --- a/lib/ioctl_wrappers.c
> >>>> +++ b/lib/ioctl_wrappers.c
> >>>> @@ -1460,7 +1460,7 @@ bool gem_has_ring(int fd, unsigned ring)
> >>>> /* silly ABI, the kernel thinks everyone who has BSD also has
> >>>> BSD2 */
> >>>> if ((ring & ~(3<<13)) == I915_EXEC_BSD) {
> >>>> - if (ring & (3 << 13) && !gem_has_bsd2(fd))
> >>>> + if (!(ring & (3 << 13)) ^ !gem_has_bsd2(fd))
> >>>> return false;
> >>>> }
> >>>
> >>> If default BSD (1)
> >>> and no BSD2 -> 1 ^ 1 = 1 OK
> >>
> >> Oops
> >> 1 ^ 1 = 0 so also bad
> >>
> >>> and BSD2 -> 1 ^ 0 = 1 BAD
> >>>
> >>> If explicit BSD (0)
> >>> and no BSD2 -> 0 ^ 1 = 1 BAD
> >>> has BSD2 -> 0 ^ 0 = 0 = BAD
> >>>
> >>> Maybe I'm confused.. please simplify the statement? :)
> >
> > return false?
> >
> > default BSD ^ has-bsd2
> > 0 0 -> 0 OK
> > 0 1 -> 1 SKIP
> > 1 0 -> 1 SKIP
> > 1 1 -> 0 OK
> >
> > So we only use bsd (implicit) on single BSD engine machines, and only
> > use bsd0,bsd1 (explicit) on dual engine machines.
>
> Don't get in your notation why is 0 OK and 1 SKIP. 0 is false = no ring
> = skip.
>
> default BSD ^ has-bsd2
> 0 0 0 ^ !0 = 1 has engine - WRONG
> 0 1 0 ^ !1 = 0 no engine - WRONG
> 1 0 1 ^ !0 = 0 no engine - WRONG
> 1 1 1 ^ !1 = 1 has engine - WRONG
>
>
> default BSD ^ has-bsd2
> 0 0 0 ^ 0 = 0 no engine - OK
> 0 1 0 ^ 1 = 1 has engine - OK
> 1 0 1 ^ 0 = 1 has engine - OK
> 1 1 1 ^ 1 = 0 no engine - OK
>
> So previous version was OK!?
Now I am confused, v2 is the one that appears to work.
Anyway, I remember why it is like this. The intention is to iterate the
ABI not the physical engines, I keep meaning to do
s/for_each_engine/for_each_uabi_ring/ and then for_each_physical_engine
that skips the aliased default and bsd (and whatever the future may
bring).
Bring on class/instance.
-Chris
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