[Intel-gfx] [PATCH 7/7] drm/i915: Engine queues query

[Chris Wilson]

Quoting Lionel Landwerlin (2018-03-31 02:04:26)
> On 19/03/18 18:16, Tvrtko Ursulin wrote:
> > From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >
> > As well as exposing active requests on engines via PMU, we can also export
> > the current raw values (as tracked by i915 command submission) via a
> > dedicated query.
> >
> > This is to satisfy customers who have userspace load balancing solutions
> > implemented on top of their custom kernel patches.
> >
> > Userspace is now able to include DRM_I915_QUERY_ENGINE_QUEUES in their
> > query list, pointing to initialized struct drm_i915_query_engine_queues
> > entry. Fields describing engine class and instance userspace would like to
> > know about need to be filled in, and i915 will fill in the rest.
> >
> > Multiple engines can be queried in one go by having multiple queries in
> > the query list.
> >
> > Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_query.c | 43 +++++++++++++++++++++++++++++++++++++++
> >   include/uapi/drm/i915_drm.h       | 26 +++++++++++++++++++++++
> >   2 files changed, 69 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
> > index 3ace929dd90f..b3bc69e8deb7 100644
> > --- a/drivers/gpu/drm/i915/i915_query.c
> > +++ b/drivers/gpu/drm/i915/i915_query.c
> > @@ -82,9 +82,52 @@ static int query_topology_info(struct drm_i915_private *dev_priv,
> >       return total_length;
> >   }
> >   
> > +static int
> > +query_engine_queues(struct drm_i915_private *i915,
> > +                 struct drm_i915_query_item *query_item)
> > +{
> > +     struct drm_i915_query_engine_queues __user *query_ptr =
> > +                             u64_to_user_ptr(query_item->data_ptr);
> > +     struct drm_i915_query_engine_queues query;
> > +     struct intel_engine_cs *engine;
> > +     const int len = sizeof(query);
> > +     unsigned int i;
> > +
> > +     if (query_item->flags)
> > +             return -EINVAL;
> > +
> > +     if (!query_item->length)
> > +             return len;
> > +     else if (query_item->length < len)
> > +             return -ENOSPC;
> 
> topology returns EINVAL in that case. I think ENOSPC makes more sense, 
> do we need to change topology?

I suggest -EINVAL, we are still doing user parameter checking. I think
we will find more useful cases for -ENOSPC later and so would prefer to
keep it clear.
-Chris