Re: [PATCH v3 3/3] drm/i915: Enable Resource Streamer state save/restore in HSW

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, May 19, 2015 at 09:58:52AM +0300, Abdiel Janulgue wrote:
> 
> 
> On 05/18/2015 07:07 PM, Ville Syrjälä wrote:
> > On Mon, May 18, 2015 at 04:41:51PM +0100, Chris Wilson wrote:
> >> On Mon, May 18, 2015 at 06:36:18PM +0300, Ville Syrjälä wrote:
> >>> On Mon, May 18, 2015 at 11:31:56AM +0300, Abdiel Janulgue wrote:
> >>>> Also clarify comments on context size that the extra state for
> >>>> Resource Streamer is included.
> >>>>
> >>>> Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>>> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
> >>>> ---
> >>>>  drivers/gpu/drm/i915/i915_gem_context.c | 2 +-
> >>>>  drivers/gpu/drm/i915/i915_reg.h         | 3 ++-
> >>>>  2 files changed, 3 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> >>>> index f3e84c4..1db107a 100644
> >>>> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> >>>> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> >>>> @@ -509,7 +509,7 @@ mi_set_context(struct intel_engine_cs *ring,
> >>>>  	}
> >>>>  
> >>>>  	/* These flags are for resource streamer on HSW+ */
> >>>> -	if (!IS_HASWELL(ring->dev) && INTEL_INFO(ring->dev)->gen < 8)
> >>>> +	if (IS_HASWELL(ring->dev))
> >>>>  		flags |= (MI_SAVE_EXT_STATE_EN | MI_RESTORE_EXT_STATE_EN);
> >>>
> >>> I don't get it. Previously we told the hardware to save the extended
> >>> context on !hsw, and now we don't. That doesn't seem correct to me.
> >>
> >> We don't use the extended state elsewhere.
> > 
> > Umm. On SNB at least 3DSTATE_POLY_STIPPLE_PATTERN seems to be part of
> > the extended state, and on IVB/VLV SOL state is there. Mesa uses all of
> > that.
> > 
> >> I'd always been dubious of
> >> the origins/intentions of this line of code since it claims only to be
> >> for enabling RS on HSW...
> >>
> >> i.e. commit e80f14b6d36e3e07111cf2ab084ef8dd5d015ce2
> >> Author: Ben Widawsky <benjamin.widawsky@intel.com>
> >> Date:   Mon Aug 18 10:35:28 2014 -0700
> >>
> >>     drm/i915: Don't save/restore RS when not used
> >>  
> >> was backwards.
> > 
> > ? It did exactly what it said, ie. avoid setting the RS save/restore
> > bits on HSW+ while leaving the ext save/restore enabled on older
> > platforms.
> > 
> 
> Another option is to enable extended state save restore for both HSW and
> the older platforms so we would get both features (RS save/restore and
> Extended State Save enable)?
> 
> Seems the reason for this confusion is that the we have the exact same
> bit positions in MI_SET_CONTEXT but it got renamed starting from HSW and up.

If the bit has been renamed it might be good to add at least a new #define
with a _HSw suffix and better name, just to make it clear what's going on.
gcc will see through this and fold down the different conditions to just
one.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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