Re: [PATCH] drm/i915: Emit even number of dwords when emitting LRIs

[Damien Lespiau <damien.lespiau@intel.com>]

On Thu, Oct 23, 2014 at 02:21:02PM +0200, Daniel Vetter wrote:
> On Wed, Oct 22, 2014 at 06:59:52PM +0100, Arun Siluvery wrote:
> > The number of DWords should be even when doing ring emits as
> > command sequences require QWord alignment.
> > 
> > v2: user LRI variant that can write multiple regs in one go (Damien).
> > We can simply insert one NOP at the end instead of one per register write.
> > 
> > Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> > Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_ringbuffer.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > index 497b836..a8f72e8 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > @@ -680,15 +680,16 @@ static int intel_ring_workarounds_emit(struct intel_engine_cs *ring)
> >  	if (ret)
> >  		return ret;
> >  
> > -	ret = intel_ring_begin(ring, w->count * 3);
> > +	ret = intel_ring_begin(ring, (w->count * 2 + 2));
> >  	if (ret)
> >  		return ret;
> >  
> > +	intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(w->count));
> 
> Afaik there's a limit to the size of an MI_LRI. Where's the check for
> that (probably with a WARN_ON for now to avoid unecessary complexity)?

I guess there's always the size of the length field, I don't see any
other indication. Note that I can find the documentation of the
multi-registers version of LRI either. So, well, we probably should
double check it does work.

-- 
Damien