[Intel-gfx] [PATCH] drm/i915: Check engine->default_state mapping on module load

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-09-14 11:03:18)
> 
> On 14/09/2018 10:51, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-09-14 10:43:12)
> >>
> >> On 14/09/2018 10:21, Chris Wilson wrote:
> >>> Check we can indeed acquire a WB mapping of the context image on module
> >>> load. Later this will give us the opportunity to validate that we can
> >>> switch from WC to WB as required.
> >>>
> >>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>> ---
> >>>    drivers/gpu/drm/i915/i915_gem.c | 11 +++++++++++
> >>>    1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >>> index be9d012d851b..37353afec66e 100644
> >>> --- a/drivers/gpu/drm/i915/i915_gem.c
> >>> +++ b/drivers/gpu/drm/i915/i915_gem.c
> >>> @@ -5424,6 +5424,7 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
> >>>    
> >>>        for_each_engine(engine, i915, id) {
> >>>                struct i915_vma *state;
> >>> +             void *vaddr;
> >>>    
> >>>                state = to_intel_context(ctx, engine)->state;
> >>>                if (!state)
> >>> @@ -5446,6 +5447,16 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
> >>>                        goto err_active;
> >>>    
> >>>                engine->default_state = i915_gem_object_get(state->obj);
> >>> +
> >>> +             /* Check we can acquire the image of the context state */
> >>> +             vaddr = i915_gem_object_pin_map(engine->default_state,
> >>> +                                             I915_MAP_WB);
> >>> +             if (IS_ERR(vaddr)) {
> >>> +                     err = PTR_ERR(vaddr);
> >>> +                     goto err_active;
> >>> +             }
> >>> +
> >>> +             i915_gem_object_unpin_map(engine->default_state);
> >>
> >> Ah this perhaps strengthens the argument to have
> >> __intel_engines_pin_default_state? (And the unpin pair.)
> > 
> > I hope it doesn't come to making this into an interface :)
> > Definitely not an idea I endorse, random manipulation of the
> > default_state.
> 
> Double underscore alleviates those concerns, no? :)

Bah, did you see the EXPORT_SYMBOL_GPL(__i915_gem_object_set_pages),
nothing is safe!
 
> Would makes it only one place the following patch needed to switch to 
> MAP_FORCE_WB.

But that was the point of having a separate step here. This is then the
only mapping of default_state that needs to do the force. I liked that.
The other one we need is the initialisation of the lrc state.
-Chris