[Intel-gfx] [PATCH] drm/i915: Emit even number of dwords when emitting LRIs

[Chris Wilson]

On Thu, Oct 23, 2014 at 01:42:38PM +0100, Damien Lespiau wrote:
> 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 at intel.com>
> > > Signed-off-by: Arun Siluvery <arun.siluvery at 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.

It does work. The max is around 60 iirc (the max length of the
command).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre